Citrus and herbs go hand in hand in this vibrant Lemon Thyme Cake. Light lemon cake if flecked with fresh thyme and layered with lemon buttercream. Add a ripple of homemade lemon curd for an extra pop of flavor and decorate with fresh thyme for a simple, rustic look.
Perhaps one day my well of cake ideas will run dry, but thankfully that day is not today. Being able to incorporate seasonal ingredients and savoury herbs into sweet treats keeps the creativity following, and today I am happily sharing this Lemon Thyme Cake.
I am not a rookie when it comes to incorporating more savoury elements into my cakes, however I think I've only scratched the surface when it comes to herbaceous sweets. My go-to is to infuse herbs into a simple syrup that gets generously brushed onto each cake layer. This time, I took a step further and added freshly chopped thyme straight into the cake batter.
Adding the fresh thyme into the cake batter really helped the flavor shine through all of the butter and sugar. But if I am being honest, I think the real star is the lemon curd buttercream.
Now, I've made lemon curd and I've made buttercream plenty of times, but the product of combining the two together proved to be otherworldly. Sometimes straight lemon curd can be a bit tricky as a cake filling, so I opted to mix it with my trusted Swiss meringue buttercream.
Swiss meringue buttercream is fairly mild in flavor, making it the perfect base for other flavorings. But seriously, lemon curd buttercream - you guys, it's like heaven! Light and lemony - not too tart, not too sweet.
But just for fun, I took a couple teaspoons of leftover curd and swirled it over the buttercream just before topping it the next layer of thyme-soaked lemon cake. Now how good does that sound?!?!
Lemon Thyme Cake
For the Lemon Curd
- 5 tablespoon fresh lemon juice
- 2 egg yolks
- 1 large egg
- ⅔ cup granulated sugar
- 5 tablespoon unsalted butter diced
For the Lemon Thyme Cake
- 3 cups cake flour
- 2 ½ teas baking powder
- ½ tea baking soda
- ½ tea salt
- 1 tablespoon minced fresh thyme, loosely packed
- 2 cups granulated sugar
- 1 tablespoon lemon zest
- 1 cup unsalted butter softened
- 3 large eggs
- 2 egg whites
- 1 tea vanilla extract
- 1 cup whole milk
- ¼ cup fresh lemon juice
For the Thyme Syrup
- ½ cup granulated sugar
- ½ cup water
- 8 to 10 sprigs fresh thyme, or small fist-full
For the Swiss Meringue Buttercream
- 6 large egg whites
- 1 ½ cups granulated sugar
- 3 cups unsalted butter softened
- 2 teas pure vanilla extract
Make the Lemon Curd
- Place the butter in a heat safe bowl. Set a mesh sieve on top of the bowl and set aside.
- Whisk together the sugar, lemon juice, lemon zest, egg yolks, and egg in a saucepan. Cook over medium heat, while stirring constantly with a heat-safe rubber spatula to keep the eggs from curdling. Cook until the lemon curd thickens enough to coat the back of a spoon or registers 170°F on a thermometer.
- Once thickened, remove the curd from the heat and strain through the mesh sieve into the butter. Stir the lemon curd until the butter melts and combines. Press a piece of plastic wrap directly to the surface of the curd and refrigerate until cool and thick.
Make the Lemon Thyme Cake
- Pre-heat oven to 350 degrees. Grease and flour two 8-inch round cake pans and set aside.
- In a large mixing bowl, sift together the flour, baking soda, baking powder, and salt. Stir in the thyme and set aside.
- In a small bowl, rub together the sugar and lemon zest until the zest begins to release its oils and the mixture is quite fragrant.
- In the bowl of an electric mixer fitted with the paddle attachment, mix the butter on medium speed until smooth. Add in the lemon sugar. Continue to mix on medium-high until the mixture is light and fluffy, about 3 to 4 minutes.
- With the mixer on low, add in the vanilla, whole eggs, and egg whites – one at a time. Stop the mixer and scrape down the sides and bottom of the bowl.
- Turn the mixer to low speed. In alternating batches (starting and ending with the dry ingredients), add in half of the flour mixture. Pour in the lemon juice and the milk and mix until combined. Add the remaining flour mixture. Mix on medium for no more than 20 to 30 seconds once the last bits of flour disappear.
- Divide the batter between to two cake pans and bake for about 25 to 28 minutes, or until a toothpick inserted into the center comes out clean. Let cool on a wire rack for 10 to 15 minutes before removing the cakes from their pans.
Make the Thyme Syrup
- Place the sugar and water in a small saucepan. Bring the mixture up to a boil, then reduce the heat. Add in the thyme and continue to simmer until the mixture thickens slightly, about 8 to 10 minutes. Let the thyme steep until cool. Strain and discard the thyme before use.
Make the Swiss Meringue Buttercream
- Place the egg whites and sugar in the bowl of an electric mixer. Whisk to combine.
- Fill a medium saucepan with a few inches of water and bring to a simmer. Place the mixing bowl on top of the saucepan to create a double-boiler. While whisking, heat the egg mixture until it reaches about 166 degrees on a candy thermometer.
- Once hot, carefully move the mixing bowl back to the mixer. Using the whisk attachment, beat the egg mixture on high until stiff peaks form and the outside of the mixing bowl returns to room temperature (about 8 to 10 minutes).
- Turn the mixer to low, and begin adding in the softened butter, a few tablespoons at a time. Once the butter has been added and begins to incorporate, swap the whisk for the paddle attachment. Add in the vanilla. Turn the mixer up to medium-high and mix until silky smooth.
To Assemble the Cake
- Make the filling by folding together 2 ½ cups of the buttercream with ½ cup of lemon curd. Set aside.
- Once the cakes have completely cooled, carefully cut each in half (horizontally) with a long, serrated knife to create four, even layers. Generously brush each layer with the thyme syrup.
- Place the bottom layer of cake on a cake plate or serving dish. Fill a pastry bag fitted with a medium plain (round) tip with some of the buttercream. Pipe a ring of frosting around the outer top edge of the cake. Fill the ring with about ¾ cup lemon filling. Dollop on a couple tablespoons of lemon curd on top and gently swirl.
- Top with the next layer of cake and repeat. Frost the cake with the remaining vanilla bean frosting. Garnish with fresh thyme, if desired.
- To create the ombre swirl effect, remove about ⅓ of the remaining buttercream. Tint that portion the desired color of choice and set aside. Top the cake with a large scoop of plain vanilla bean frosting and smooth out, allowing for some of the frosting to get pushed over the sides. Take the tinted frosting and apply it to the bottom ⅓ of the cake with an off-set spatula.
- Mix the tinted buttercream with any remaining buttercream to create a lighter shade (add more coloring, if necessary). Fill in the sides of the cake with the lighter frosting. Once the cake is covered in buttercream, smooth out the sides with an icing smoother, off-set spatula, or bench scraper.
- For the swirled effect, place the cake on top of a cake turntable. Touch the tip of a metal spatula to the bottom of the cake. Rotate the turntable and move the spatula straight up the side of the cake. For the top, place the tip of the spatula near the outer edge. Rotate the turntable and move the spatula towards the center of the cake to create a swirl.