Preheat oven to 350°F. Butter one 8 inch round cake pan. Set aside.
In a medium bowl, whisk together flour, cocoa powder, baking powder, baking soda and salt.
In a medium saucepan over medium high heat, combine water and sugar. Bring to a boil and stir until sugar dissolves, about 1 minute. Remove from heat and add chocolate and butter, stirring occasionally, until melted.
Whisk in vegetable oil and vanilla extract. Quickly beat in eggs (do this quickly so they don’t cook) into the chocolate mixture until combined. Whisk in dry ingredients, until smooth.
Pour batter into prepared pan and bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean.
Let cake cool in pan until cool to the touch – then frost.
Peanut Butter Frosting:
Cream butter and peanut butter in a stand mixer. Add vanilla and salt. Gradually add powdered sugar, one half cup at a time, beating well on medium speed. Scrape sides and bottom of bowl as needed.
When all sugar has been mixed in, icing will appear dry. Add milk, one teaspoon at a time, and beat at medium speed until light and fluffy.
Spread one thick and even layer on the top of the cake. Then prepare the chocolate glaze.
Dark Chocolate Glaze:
Combine butter, milk, corn syrup, and vanilla extract in small saucepan and heat over medium heat until butter is melted. Decrease the heat to low, add the chocolate, and whisk until melted.
Remove from heat, add the powdered sugar, and whisk until smooth. Let chocolate glaze sit for 5 minutes until it has cooled slightly and started to thicken just a little bit. Then slowly pour on top and push towards the edges – allowing a little to drizzle over the edge for desired effect.
Let glaze harden for 30 minutes, top with chopped Reese’s cups and serve! (To Store: Keep in an airtight container for up to 3 days.)