Place the butter in a small saucepan over medium heat. Let it melt completely, then continue cooking, swirling the pan occasionally, for about 4 to 5 minutes. The butter will foam and then turn golden amber with a nutty aroma.
Once you see golden brown bits on the bottom and it smells toasty, immediately pour the browned butter into a heatproof bowl. Let it cool for 10 minutes. Preheat your oven to 350F and line an 8x8-inch baking pan with parchment paper.
Add the golden erythritol and vanilla extract to the browned butter and whisk until smooth. Beat in the eggs one at a time until well combined.
In a separate bowl, whisk together the almond flour, coconut flour, baking powder, and salt. Add the dry ingredients to the wet mixture and stir until a thick batter forms. Fold in the sugar-free chocolate chips.
Spread the batter evenly into the prepared pan. Sprinkle a pinch of flaky sea salt over the top.
Bake for 22 to 25 minutes until the top is golden and the edges are set but the center still looks slightly soft. Let the bars cool completely in the pan before slicing into 12 bars. The center will firm up beautifully as they cool.
