Preheat oven to 350ºF. Butter two 9-inch round cake pans, and dust with flour, tapping out excess.
Combine flour, sugars, cocoa, baking soda, baking powder, and salt into the bowl of a mixer. Mix on low. Add eggs, buttermilk, coffee, oil, and vanilla. Beat on medium speed until smooth and completely combined.
Divide batter evenly among pans. Bake until cakes are set and a toothpick inserted into the center of each comes out clean, about 35 minutes. Let cool in pans set on a wire rack for 15 minutes. Turn out cakes onto racks, and let cool completely.
For the raspberry filling
In the bowl of a stand mixer, fitted with paddle attachment (or any large mixing bowl, if using hand-held beaters), beat the butter on medium-high speed until creamy, about 3-5 minutes. Add the raspberry jam and beat to combine. Turn the mixer down to low speed, and add the powdered sugar. Beat until smooth. Cover and set aside until ready to use.
For the mocha buttercream
Place room temperature butter and vanilla into a stand mixer and beat at medium-high for about three minutes.
Add cocoa, instant coffee and salt to the bowl beat into the butter until the coffee has broken down and the mixture is smooth, 1-2 minutes.
Add in one cup of the powdered sugar. Turn mixer on to low and then slowly add in remaining powdered sugar.
With mixer still on low, slowly drizzle in the heavy cream. Turn mixer to medium high and mix for 2-3 minutes, or until light and fluffy.
On a cake plate or board, place one cake layer. Spread raspberry buttercream filling evenly on top of the cake using an offset spatula.
Carefully place the other cake layer top-down on the frosting, so the top is flat. Adjust the cake so that the sides are lined up evenly.
Frost the entire outside of the cake with a thin layer of the chocolate mocha buttercream. Place in the refrigerator for 30 minutes to lock in the crumb coat.
Frost the cake as desired, and arrange raspberries on top of the cake. Dust with powdered sugar if desired.