Preheat the oven to 350 degrees. Grease and flour an 8-inch square pan.
In a saucepan, melt the butter. Add the chocolate chips and cocoa powder. Mix until combined and the chocolate is perfectly melted, then remove from heat.
In a standing mixer, mix the eggs until they are light and fluffy. Add the sugar little by little, and beat until the eggs are lighter in color.
Add the cooled chocolate mixture into the bowl with the sugar and eggs. Add the vanilla. Mix until combined.
Sift the flour into the mixture and mix until combined. Do NOT over mix. You can also mix it manually instead of using the standing mixer.
Pour the batter into your lined baking pan and spread around until the entire bottom of the pan is filled.
Bake in the oven for 20 - 25 minutes or until the texture does not bounce, and it doesn't look shiny anymore. Allow the brownies to cool for 10 minutes before removing from the pan.
Remove the brownies from the pan and allow to cool completely. Make a grid on top for cutting into triangles as shown.
Once you have a grid, cut the brownies. There should be three rows, 4 large triangles per row, so they are even, and you will have some edges that can work for smaller trees. You will make 12 large brownie trees.
If you are using candy canes, unwrap each one and 1.5 inch long pieces. Press the sharper ends of the candy cane into the bottom of each brownie tree.
Buttercream Frosting
Prepare your buttercream frosting by beating the butter with a hand mixer, until light and fluffy.
Add the powdered sugar little by little until fully combined. Add the milk and mix until combined.
Add several drops of food coloring until the frosting is the green you desire.
Decorate the Brownies
Get a piping bag ready with the tip of your choice. Place the green frosting into the piping bag.
Starting at the top of the tree, gently squeeze your piping bag to make a zigzag from the top to bottom of the brownie.
Add your favorite Christmas sprinkles on top of the buttercream frosting and let set before serving.
Notes
To make the frosting flavored, you can add a teaspoon of peppermint extract or vanilla extract when you mix in the powdered sugar and milk.