Preheat your oven to 350°F (175°C) and line a 9x13-inch baking pan with parchment paper.

In a large saucepan, melt the unsalted butter over low heat, then remove it from the stove.

Stir in both the granulated sugar and brown sugar until well combined.

Add the eggs, one at a time, stirring well after each addition, then mix in the vanilla extract.

Sift in the flour, cocoa powder, baking powder, and spices, then fold gently until combined.

If using, fold in the chocolate chips until just incorporated.

Pour the batter into the prepared baking pan and smooth the top with a spatula.

Bake in the preheated oven for 25-30 minutes or until a toothpick inserted in the center comes out with moist crumbs.

Allow the brownies to cool in the pan for about 15 minutes, then lift them out using the parchment paper and let them cool completely on a wire rack.

Cut into squares and serve, optionally dusted with powdered sugar for a festive touch.