Preheat your oven to 350°F (175°C). Cover an 8x8-inch baking dish with parchment paper, ensuring a bit of overhang on the sides to make lifting out the dessert easier.
In a large mixing bowl, whisk together the all-purpose flour, cocoa powder, baking powder, and brown sugar until well combined.
In a separate bowl, whisk the almond milk, melted coconut oil, and maple syrup until smooth.
Gradually add the wet mixture to the dry ingredients, pouring it in slowly.
Gently fold until just combined. Take care not to overmix, as doing so may compromise the brownies' texture.
Evenly distribute the brownie batter in the lined pan using a spatula.
Add spoonfuls of peanut butter on top, spacing them across the surface. Drag a knife or skewer through the peanut butter and batter to create a swirled, marbled pattern.
Bake in the preheated oven for 25-30 minutes. Test for doneness by inserting a toothpick into the center—it should emerge with a few moist crumbs clinging to it, but without any wet batter.
Allow the brownies to cool completely in the pan before slicing. For cleaner slices, refrigerate them for 30 minutes before cutting.