My husband picked this cake from 
Brown Eyed Baker for his birthday cake. The cakes are moist and full of chocolate flavor. The frosting is amazing and delicious. This is a mighty tasty cake. Well chosen, David, well chosen.
All told, this is less than 2 hours of time to create. I baked the cakes in advance and froze them for easy frosting that I did in about 30 minutes. I tossed the cake in the fridge while we went out to meet Dave at work for a quick lunch and then made the ganache when we got home. 
Chocolate Peanut Butter Cup Cake
Cake 
2 1/2 cups + 1 Tbsp. flour
3 cups sugar
1 cup + 1 Tbsp. Dutch-process cocoa powder
1 Tbsp. baking soda
1 1/2 tsp. baking powder
1 1/2 tsp. salt
3 eggs, room temperature
1 1/2 cups buttermilk, room temperature
1 1/2 cups boiling water
3/4 cup vegetable oil
4 1/2 tsp. vanilla
 
Peanut Butter Frosting
2 cups powdered sugar
2 cups creamy peanut butter
10 Tbsp. butter, room temperature
1 1/2 tsp. vanilla
1/4 tsp. salt
1/3 cup heavy cream
 
Chocolate Ganache
8 oz. semi-sweet chocolate, finely chopped
3/4 cup heavy cream
Garnish
30 mini peanut butter cups
To bake the cakes, preheat oven to 350°F. Grease three 8-inch round cake pans,
 line the bottoms with rounds of parchment paper, grease the parchment, 
then flour the insides of the pans and tap out excess. Set aside.
In the bowl of a large electric mixer, sift together the flour, sugar, cocoa powder, 
baking soda, baking powder and salt. In a medium bowl, whisk together 
the eggs, buttermilk, water, oil and vanilla.
Add the wet ingredients to the dry ingredients, and mix for 2 minutes
 on medium speed. Scrape the sides and bottom of the bowl, and mix for an
 additional 20 seconds. (Let me just say ... this was the biggest mess I think I've ever created. My standard mixing bowl was not large enough for this recipe.)
Divide the batter evenly among prepared pans. Bake for 20 minutes, 
and rotate the pans in the oven. Continue to bake until a toothpick 
inserted into the center of one of the cakes comes out almost clean 
(with a few moist crumbs), about 12 more minutes. Cool the cakes (in the
 pans) on wire racks for 20 minutes, and then carefully turn them out onto 
cooling racks to cool completely.
To make the frosting, place the powdered sugar, peanut butter, butter, vanilla and salt in 
the bowl of an electric mixer fitted with a paddle attachment. Mix on 
medium-low speed until creamy, scraping down the bowl with a rubber 
spatula as needed. Add the heavy cream, and beat on high speed until the 
mixture is light and smooth.
If your cakes baked up uneven or have domed on top, level the cakes. Place one cake layer on a serving plate. Cover with 1 cup of the 
peanut butter frosting, and sprinkle 10 of the chopped peanut butter cups
 over the frosting. Top with a second cake layer, and cover with another 1
 cup of the peanut butter frosting, and top with another 10 chopped 
peanut butter cups. Place the final cake layer on top face-down. Frost 
the cake with the remaining peanut butter frosting, finishing it as 
smoothly as possible. Refrigerate the cake for at least 1 hour, until 
the frosting is set.
While the cake chills, make the chocolate ganache. Place the chocolate 
in a 4-cup measuring cup; set aside. Place the cream in a small saucepan
 over medium heat, and warm until it just comes to a boil. Pour the cream
 over the chopped chocolate, and let sit for 2 minutes. Begin whisking 
the mixture in the center, gradually working your way outward until the 
ganache is completely smooth. Set aside to cool, whisking occasionally, 
until it has thickened slightly, yet still a pourable consistency.
Slowly pour the chocolate ganache into the center of the cake, 
letting it push itself outward and flow over the sides of the cake. Top 
with the remaining 10 chopped peanut butter cups. Refrigerate the cake 
for at least 30 minutes, giving the ganache a chance to set up. Keep the
 cake refrigerated, removing it from the refrigerator about 20 minutes 
prior to serving.