Preheat oven to 350°F (175°C). Line a 10×15-inch jelly roll pan with parchment paper and lightly grease it. Sift flour, cocoa powder, baking powder, and salt into a bowl. Beat eggs and granulated sugar with an electric mixer until light and fluffy (5 minutes). Add vanilla and milk, then gently fold in the dry ingredients. Spread the batter evenly into the pan and bake for 10–12 minutes until the cake springs back when touched. Invert the warm cake onto a kitchen towel dusted with powdered sugar. Remove parchment and roll gently from the short end. Let cool completely. In a bowl, mix peanut butter, powdered sugar, butter, vanilla, and chopped Reese’s cups until creamy. Spread the filling over the unrolled cake and re-roll it with the towel, placing it seam-side down. For ganache, microwave chocolate chips and heavy cream in 20-second intervals until smooth, then pour over the cake.