Preheat Oven: Preheat your oven to 350°F (175°C). Line an 8×8-inch (20×20 cm) baking pan with parchment paper, leaving an overhang on the sides for easy removal.
Melt Butter and Chocolate: In a large microwave-safe bowl, combine the melted butter and chopped semi-sweet chocolate. Microwave until completely melted and smooth, stirring every 30 seconds.
Add Sugar: Stir the granulated sugar into the melted butter and chocolate mixture until well combined.
Beat thoroughly after adding each of the seasonings and eggs one at a time. Then, mix in the vanilla extract, white vinegar, and red gel food coloring until the batter is evenly colored.
Combine Dry Ingredients: In a separate bowl, sift together the unsweetened cocoa powder, all-purpose flour, and salt.
Blend the Batter: Slowly stir the dry ingredients into the wet mixture until they are just blended. To keep the texture fudgy, take care not to overmix. If using, fold in the white chocolate chips.
Bake: Evenly distribute the batter after pouring it onto the baking pan. A toothpick inserted in the center should come out with a few moist crumbs after baking for 30 to 35 minutes in a preheated oven.
Let the brownies cool fully in the pan on a wire rack before serving. Once cooled, lift them out using the parchment overhang, cut into 16 squares, and serve.