Once all of the cakes (including the brownie) have completely cooled, use a serrated knife to carefully split them in half. There will be 6 layers total.
Place one layer of cake on a cake board or serving dish. Fill a piping bag fitted with a medium round tip with the Nutella buttercream. Pipe a ring of buttercream around the outer edge of the cake. Fill the center of the buttercream “dam” with 3 to 4 tablespoons of raspberry jam. Smooth out with an offset spatula.
Top the raspberry filling with a second layer of cake. Dollop on about ¾ of Nutella buttercream and spread until smooth with an offset spatula.
Place one of the brownie cake layers on top and repeat with the Nutella buttercream dam and raspberry filling. Place the second brownie cake layer on top. Dollop on about ¾ of Nutella buttercream and spread until smooth with an offset spatula.
Place another cake layer on top and repeat with the Nutella buttercream dam and raspberry filling. Finally, place the last cake layer on top.
Crumb coat the cake with buttercream and chill in the refrigerator for 15 minutes.
If the cake starts to get too soft at any point during the stacking process, place the whole thing in the fridge or freezer until the buttercream firms up slightly. You may also crumb coat the sides of the cake as you stack by spreading a thin layer of buttercream around the cake to ensure that none of the raspberry jam leaks out.
Frost the crumb coated cake with Nutella buttercream until smooth. Chill for about 10 minutes.
Using a spoon or squeeze bottle, add the chocolate drip around the edges of the cake. The glaze needs to be room temperature but still liquid.
Fill a piping bag fitted with a star tip with the remaining buttercream. Pipe spiral of buttercream around the top edge of the cake. Place a fresh raspberry on top of each spiral.