Preheat oven to 350°F (175°C). Grease an 8x8 inch baking pan with butter or non-stick spray. Line with parchment paper, leaving overhang on two sides.

In a large mixing bowl, combine melted butter and granulated sugar. Whisk until well incorporated.

Add vegetable oil and whisk again.

Add eggs one at a time, whisking well after each.

Stir in buttermilk, vanilla extract, and white vinegar.

Add green food coloring and mix until desired color is achieved.

In a separate bowl, whisk together flour, cocoa powder, baking soda, and salt.

Fold dry ingredients into wet ingredients gently, until just combined.

Pour batter into prepared pan and spread evenly. Bake for 25-30 minutes, until toothpick comes out with moist crumbs.

Cool completely in pan on wire rack.

Beat cream cheese and butter until smooth.

Add powdered sugar gradually, mixing on low.

Add vanilla and salt, then mix on medium-high until light and fluffy.

Spread frosting over cooled brownies.

Add sprinkles if desired. Slice into squares and serve.