Preheat your oven to 350°F (175°C) and line an 8x8 or 9x9 inch pan with parchment paper. In a large mixing bowl, melt 2 cups of unsalted butter and combine it with 2 cups of granulated sugar, 4 room temperature eggs, and 1 teaspoon of vanilla extract. Fold in the melted butter along with 1 cup of all-purpose flour, 1 cup of unsweetened cocoa powder, ½ teaspoon of baking powder, and ¼ teaspoon of fine sea salt. Pour the batter into the prepared pan and bake for 25-35 minutes, until a toothpick inserted shows moist crumbs. Allow to cool for 2-3 hours.

In a clean mixing bowl, beat 1 cup of softened unsalted butter on medium speed until fluffy. Gradually mix in 4-5 cups of sifted powdered sugar, then add 3-5 tablespoons of heavy cream, 1 teaspoon of vanilla extract, and a pinch of salt. Beat until the frosting is smooth and airy, adjusting the cream for your preferred consistency. Color the frosting with gel food coloring.

Once your brownies are completely cooled, spread an even layer of the buttercream frosting over the top. Chill them in the refrigerator for about 30 minutes until the frosting firms up. Pipe melted candy melts in ribbon shapes across the frosting and sprinkle festive decorations like edible glitter.

Once decorated and chilled, cut the brownies into squares or rectangles. Store any leftovers in an airtight container at room temperature for 3-4 days, or refrigerate for up to a week. Optionally, freeze them for 1-2 months.