Preheat oven to 350 F degrees. Grease and flour 2 8in cake pans.
In a medium sauce pan, melt the butter. Add the coffee, espresso powder, cocoa powder, and vanilla and whisk until combined. Set aside to cool slightly.
In a large bowl, sift together the sugar, flour, baking soda and salt. Set aside.
In a medium bowl, whisk together the sour cream and the eggs. SLOWLY add a few tablespoons of the chocolate mixture to the sour cream and eggs. Whisk to combine. In a slow stream, whisk in the remaining chocolate mixture until combined completely.
Make a well in the center of the flour mixture and pour in wet. Using a whisk, stir until no more lumps remain.
Divide the batter evenly into the prepared pans. Each pan should get half of the batter. Bake 23-25 minutes or until a toothpick comes out clean. Cool in pan for 10 minutes before removing from the pans to cool on a wire rack.
Once the cakes have cooled, but are still warm, using a cake leveler to cut off the round mound on the top of the cake. Make sure all four layers are the same size.
In a large pan, melt the butter.
Add the raspberries, sugar and lime and bring to a simmer over medium-high heat. Stir continuously so that the raspberries begin to break down.
Add the corn starch and stir to combine. Continue to cook until the raspberries thicken, about 2 minutes.
Stir in the salt.
Remove from heat and allow to cool completely before filling cake.
Whipped Vanilla Buttercream:
In the bowl of your stand mixer, cream the butter until smooth.
One cup at a time, add the powdered sugar and mix until smooth.
Mix in the vanilla extract and pinch of salt.
Add enough heavy cream until you reach your desired consistency. You're looking for light and soft but still holds its shape.
Mix on high for about 3-5 minute until light and fluffy.
Place one layer of cake on a cake stand/board. Trim the top until it is flat.
Pipe a small border of frosting around the outside edge of the cake. Fill the middle with the raspberry mixture.
Trip the top of the second cake layer until flat. Gently press it trimmed side down onto the raspberry layer.
Pipe or spread the remaining frosting onto the outside edge of the cake and smooth out with a spatula.