1cup(2 sticks) unsalted buttersoftened to room temperature
1cupfirmly packed light brown sugar
1cupGreek yogurtany fat content
CHOCOLATE GANACHE FILLING
8ouncesquality semi-sweet chocolatefinely chopped
1/2cup(1 stick) unsalted buttersoftened to room temperature
1-7ouncecontainer marshmallow creme
1 and 1/2cupspowdered sugar
GRAHAM CRACKER CAKE
Preheat the oven to 350ºF. Generously grease and flour (or use homemade cake release) two 8" round cake pans.
In a medium size bowl, toss together the graham cracker crumbs, flour, baking powder, baking soda, and salt. Set aside.
In a large bowl with a handheld mixer or the bowl of a stand mixer fitted with the paddle attachment, cream both sugars and butter until light and fluffy (approximately 3 minutes). Add the eggs one at a time, insuring each egg is completely combined before adding the next, and beat on medium speed until smooth. Add the vanilla, and beat again until combined. Scrape down the sides and bottom of the bowl with a spatula. Turn mixer speed to low and slowly add the graham cracker in 2 additions, alternating with the Greek yogurt. Beat until completely combined.
Pour the batter evenly between the two prepared cake pans. Bake for 28-30 minutes or until a toothpick inserted in the center comes out mostly clean. Remove from oven and allow cakes to cool in the pans completely on a wire rack before removing and assembling.
CHOCOLATE GANACHE FILLING
Place the finely chopped chocolate into a medium size bowl. Set aside.
In a small saucepan over medium heat, combine the heavy cream and butter and heat to steam. Remove from heat and immediately pour over the bowl of chocolate. Allow to sit for a few minutes, then carefully stir mixture until all of the chocolate is melted. Allow to cool completely at room temperature before using.
In a large bowl with a handheld mixer or the bowl of a stand mixer fitted with the paddle attachment, cream the butter until it is light and fluffy. Add the marshmallow creme and beat on high until smooth (approximately 2 minutes).
With the mixer on low, add the powdered sugar. Increase mixer speed to medium and beat until completely combined (approximately 1 minute).
Trim cooled cake layers to create a flat surface. You can do this with a large serrated knife or a cake leveler. I cut each layer in half so I had 4 layers total. Place one layer on a plate or cake stand and cover the top with chocolate ganache. Spread evenly with an offset spatula. Repeat this step until you have used all of your layers, placing the very top layer cut surface down.
For a sturdier cake, refrigerate at this point for about 10 minutes. When cake is slightly chilled, remove from refrigerator and spread a generous layer of marshmallow buttercream on the top of the cake. Spread a thinner layer around the sides. Use a kitchen torch to toast just the top of the cake (the sides will melt). Leftovers stay fresh, covered at room temperature up to 3 days and in the refrigerator up to 5 days.
Make ahead: prepare cakes and frosting up to 1 day in advance. Cover cakes tightly and keep at room temperature or in the refrigerator until ready to assemble. Unfrosted cake layers may be frozen, wrapped tightly, up to 2 months.