Preheat your oven to 350 degrees F and grease three 9 inch cake pans really well so your layers release nice and easy.

In a large bowl, whisk together your cake flour, granulated sugar, brown sugar, cocoa powder, baking powder, and salt until everything is evenly combined.

In a separate large bowl or big measuring cup, whisk together the whole milk, sour cream, melted butter, eggs, and vanilla until it's fully combined and smooth.

Fold the wet ingredients into your dry ingredients until just combined, then pour in the hot coffee and stir it in. Your batter is going to be VERY thin, and I promise that is exactly what we want for a moist, fudgy cake!

Divide the batter evenly between your three greased pans and bake at 350 degrees F for 20 to 22 minutes, or until a toothpick inserted in the center comes out clean.

Let the cakes cool in the pans for about 10 minutes, then carefully turn them out onto wire racks and let them cool COMPLETELY, about 50 minutes. Do not rush this, warm cake plus frosting equals a melty mess!

While the cakes cool, make your ganache. Chop your dark chocolate and pop it in a bowl. Microwave your heavy cream in 20 second increments until it's warm, then pour it right over the chocolate. Let it sit untouched for 3 minutes, then stir it all together until smooth and glossy. Set it aside to thicken up, this is the part you want to give plenty of time!

Now make your frosting. Beat the peanut butter, cream cheese, and butter together until it's light, fluffy, and fully combined. Add in the heavy cream and vanilla and mix again, then slowly add your powdered sugar until you reach that perfect pipeable consistency. Set aside.

Make your chocolate simple syrup. In a small saucepan, stir together the water, granulated sugar, and cocoa powder. Let it simmer for 5 to 10 minutes, then set it aside to cool. This keeps every layer extra moist and delicious!

Time to assemble! Chop up your 20 Reese's cups. Place your first cake layer down and brush it generously with the chocolate simple syrup. Add a layer of peanut butter frosting, then a layer of ganache, then about one third of your chopped Reese's. Repeat this two more times with your remaining layers, using one third of the frosting, ganache, and Reese's each time.

Do a light crumb coat of the peanut butter frosting around the edges of the cake, then spread the ganache over the top. Swirl the remaining peanut butter frosting into a pretty design on top, and finish with a big sprinkle of chopped Reese's cups to garnish. And that is IT, the most perfect decadent cake ever!