Preheat your oven to 350°F (175°C).

Prepare your baking pan with parchment paper or grease it well.

In a medium bowl, whisk together the flour, cocoa powder, baking powder, baking soda, salt, and spices.

In a large bowl, melt the butter and mix with brown sugar and granulated sugar until well combined.

Add the eggs one at a time, followed by the vanilla extract, mixing well after each addition.

Gradually fold the dry ingredients into the wet ingredients until just combined; do not overmix.

If using, fold in the nuts at this stage.

Pour the brownie batter into the prepared baking pan, smoothing the top with a spatula.

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

Allow the brownies to cool in the pan before transferring them to a wire rack to cool completely.

Slice into squares and enjoy!