Preheat your oven to 350°F (175°C). Line an 8x8 inch baking pan with parchment paper.
In a large bowl, whisk together the melted butter, 1/4 cup peanut butter, and golden monk fruit sweetener until smooth and well combined. Add the eggs and vanilla extract and whisk vigorously until the mixture is thick and glossy.
Add the almond flour, baking powder, and salt. Stir with a spatula until a thick batter forms. Fold in the sugar-free dark chocolate chips.
Spread the batter evenly into the prepared pan. Warm the remaining 2 tablespoons of peanut butter in the microwave for about 15 seconds until very runny. Drizzle it over the batter in lines.
Use a toothpick or the tip of a small offset spatula to drag through the peanut butter lines, creating a beautiful swirl pattern across the entire surface.
Bake for 22 to 26 minutes, until the top is golden and the edges look set. The center may seem slightly soft but will firm up as it cools.
Sprinkle flaky sea salt over the top while warm. Let cool completely in the pan for at least 45 minutes before cutting into 16 squares.