Preheat oven to 350°F (175°C). Line an 8x8 inch baking pan with parchment paper, leaving an overhang on two sides for easy removal.
In a large bowl, whisk together the melted butter and erythritol until well combined. Add the eggs one at a time, whisking after each addition. Stir in the vanilla extract.
Add the almond flour, cocoa powder, salt, and baking powder to the wet mixture. Stir with a spatula until a smooth, thick batter forms with no dry pockets remaining.
Fold in the sugar-free chocolate chips, reserving a small handful for the top.
Pour the batter into the prepared pan and spread it into an even layer. Press the reserved chocolate chips gently into the surface.
Bake for 18 to 22 minutes, until the edges look set and a toothpick inserted into the center comes out with moist crumbs, not wet batter. Be careful not to overbake.
Let the brownies cool completely in the pan before lifting out and slicing into 16 squares. They firm up significantly as they cool, becoming perfectly fudgy.
