Preheat oven to 350°. Butter and lighlty flour a 9"x13" pan. (I prefer glass for the pan). Set pan aside.
Mise en place.
Melt the butter in the microwave.
Pour into large bowl (of stand mixer, if you have one). Whisk in oil, sugar, eggs, vanilla extract, and mint extract.
Beat in flour, cocoa powder, salt, and baking powder.
Spread in prepared pan. Bake for 22-25 minutes, until a toothpick comes out clearn with a few crumbs (not wet mix).
Place on cooling rack and cool completely.
Mint Layer
Whip together softened butter and softened cream cheese until completely smooth.
Whip in powdered sugar until smooth.
Add mint extract and green food coloring. Mix until smooth.
Spread over cooled brownies. Place in fridge to cool for at least 15 minutes.
Chocolate Ganache
Place chocolate chips, whipping cream, and butter into a microwave-safe bowl.
Heat for 1 minute. Remove from microwave and whip.
If needed, heat for another 30 seconds. Whip, whip, whip until smooth. (Can microwave more if needed, but keep in mind it will get smoother the longer you whip, not the longer you heat).
Spread over mint filling.
Place in fridge to cool for at least 15 minutes or until chocolate ganache level set.