Prep the pan: Heat your oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment, leaving overhang on two sides for easy lifting. Lightly grease the parchment.

Melt the butter: In a medium bowl, microwave butter in 20-second bursts until melted but not sizzling. Let it cool for 2–3 minutes so it doesn’t scramble the eggs.

Whisk in sweetener: Add the granulated low carb sweetener to the warm butter and whisk until combined. This helps it dissolve and improves texture.

Add eggs and vanilla: Whisk in eggs one at a time until the mixture looks glossy. Stir in vanilla extract.

Combine dry ingredients: In a separate bowl, whisk almond flour, cocoa powder, salt, and baking powder. Break up any almond flour lumps for a smooth batter.

Make the brownie batter: Add dry ingredients to wet and stir just until no dry spots remain. Fold in sugar-free chocolate chips if using. The batter will be thick.

Spread into the pan: Scoop the batter into the prepared pan and smooth the top with an offset spatula or the back of a spoon.

Mix the peanut butter swirl: In a small bowl, stir together natural peanut butter, powdered sweetener, and 1–2 tablespoons of heavy cream or almond milk. You want a pourable but not runny consistency. Add a pinch of salt if your peanut butter is unsalted.

Swirl it: Dollop the peanut butter mixture in 8–10 spoonfuls across the brownie batter. Use a butter knife or skewer to gently drag through the dollops in figure-eight motions. Do not overmix—you want distinct ribbons.

Bake: Bake for 18–24 minutes, depending on your oven. Start checking at 18 minutes. The center should be set with a slight jiggle, and a toothpick should come out with a few moist crumbs, not wet batter.

Cool completely: Let the brownies cool in the pan on a rack for at least 45–60 minutes. For clean slices, chill for 30 minutes after cooling.

Slice and serve: Lift out using the parchment overhang and cut into 12–16 squares. Wipe the knife between cuts for neat edges.