Line a 9-inch springform pan with parchment paper or lightly brush with butter so your brownies slide out easily later. In a large bowl, whisk together the eggs, extra yolk, brown sugar, granulated sugar, and vanilla until smooth and slightly fluffy, this gives your brownies a soft, tender bite.

In a microwave-safe bowl, melt the chocolate chips and butter in short 30-second bursts, stirring gently each time until shiny and smooth.

Pour the chocolate mixture into the sugar-egg mixture and fold gently with a spatula until just combined. You want every bite rich and chocolatey without becoming heavy.

Sift in the flour, cocoa, and optional espresso, and fold until almost combined, a few streaks of flour are perfectly fine and will bake out.

Pour the batter into your prepared pan and smooth the top. Bake at 350°F (175°C) for about 35 minutes. Keep an eye on them near the end, the center should still have a hint of goo for that perfect fudgy texture. Let the brownies cool in the pan for around 30 minutes before removing.

While the brownies cool, beat the softened butter until light and fluffy. Add vanilla, then gradually mix in powdered sugar. Stir in milk one tablespoon at a time until the frosting reaches a smooth consistency. Add a few drops of green food coloring.

Once cooled, cut the brownies into triangle shapes. Pipe the frosting using a star tip and sprinkle on your decorations or extra chocolate chips. Your little chocolate trees are now ready to enjoy, festive, fun, and totally irresistible!