Preheat the oven to 350°F. Grease two 9-inch round cake pans and line the bottoms with parchment paper.
In a large bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda and salt until no cocoa lumps remain.
Add the buttermilk, yogurt, oil and vanilla and beat on medium for 1 minute until thick and smooth.
With the mixer on low, slowly pour in the hot coffee and mix until combined. The batter will be thin, which is exactly what makes this cake so moist. Divide it evenly between the pans.
Bake for 30-35 minutes, until a toothpick inserted in the center comes out clean. Cool in the pans for 10 minutes, then transfer to a wire rack and cool completely.
For the frosting, beat the butter and peanut butter for 2 minutes until creamy. Add the powdered sugar, heavy cream, vanilla and salt, then beat on high for 2 minutes until fluffy.
Place one cake layer on a plate, spread with frosting and top with the second layer. Frost the top and sides smoothly, then chill for 20 minutes.
For the ganache, heat the cream until steaming, pour it over the chocolate chips and let sit for 3 minutes. Stir until smooth and let cool for 10 minutes to thicken slightly.Spoon the ganache over the top of the chilled cake, nudging it to the edges so it drips down the sides, then top with the peanut butter cups.