Preheat your oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment paper and lightly grease.
In a medium bowl, whisk together almond flour, coconut flour, cocoa powder, low-carb sweetener, baking powder, and salt until evenly mixed.
In another bowl, lightly beat the eggs, then add melted butter, vanilla extract, and almond milk. Mix until smooth, ensuring the melted butter isn’t too hot.
Pour the wet ingredients into the dry and fold gently until a thick, fudgy batter forms. Add chocolate chips, nuts, or peanut butter swirls if desired, folding carefully.
Spread the batter evenly in the prepared pan and bake 25–30 minutes, or until a toothpick comes out mostly clean with slightly moist crumbs. Avoid overbaking to keep them chewy.
Cool completely in the pan before slicing. For extra fudginess, chill 15–20 minutes in the refrigerator before cutting.