Line a square 8-inch baking dish with wax paper so that you have a wax paper overhanging on both sides. This will allow for easy removal later on.
Melt the butter in a medium microwave-safe bowl. Allow to slightly cool.
Mix in the stevia, peanut butter, and almond flour. Start mixing with a rubber spatula, then use a whisk to mix thoroughly until smooth and no almond flour lumps remain.
Use the spatula to transfer the mixture to the prepared pan, and to spread the mixture evenly. Freeze for 15 minutes.
Place the chocolate chips and the butter in a microwave-safe bowl. Microwave in 30-second increments, stirring after each microwave session, until almost fully melted. Stir the mixture with a rubber spatula until fully melted.
Pour the melted chocolate on top of the peanut butter layer, using the spatula to scrape it off the bowl and to spread in evenly. Work gently, so that the chocolate layer stays on top of the peanut butter layer.
Cover the pan with plastic wrap. Refrigerate until set and firm, about 4 hours.
Carefully lift the wax paper and place it on top of a cutting board. Using a sharp chef’s knife, cut into 16 squares.
Keep leftovers refrigerated in an airtight container, separated by layers of wax paper. Remove them from the fridge 5-10 minutes (but no longer, or they become too soft) before serving.