In a medium saucepan over low heat, melt the butter and semi-sweet chocolate chips together, stirring often until smooth. Remove from the heat and let it cool slightly.

Whisk the maple syrup, eggs, and vanilla extract into the melted chocolate mixture until smooth.

Stir in the oat flour, cocoa powder, and salt until just combined. The batter should be thick and glossy.

Pour the brownie batter into the prepared pan and spread it evenly. Drop spoonfuls of creamy peanut butter over the top, then gently swirl it into the batter with a butter knife or toothpick.

Bake for 25-30 minutes, or until the edges are set and the center no longer jiggles. A toothpick inserted near the center should come out with moist crumbs.

Let the brownies cool completely in the pan before lifting them out and slicing into squares.