Preheat the oven to 350°F. Line an 8x8-inch baking dish with parchment paper and lightly spray with nonstick cooking spray.
Place half of the chocolate chips in a large microwave-safe bowl. Microwave in 30-second intervals, stirring after each interval, until melted and smooth. Let cool for a few minutes.
In a separate bowl, whisk together the flour, cocoa powder, erythritol, baking powder, and salt.
Add the Greek yogurt, egg, milk, and vanilla extract to the slightly cooled melted chocolate. Whisk until smooth and combined.
Add the dry ingredients to the chocolate mixture and stir just until combined. Do not overmix.
Fold in the remaining chocolate chips.
Spread the batter evenly into the prepared baking dish.
Bake for 20–23 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Let the brownies cool in the pan on a wire rack for 20–30 minutes.
Cut into 16 squares and serve.
Notes
Do not overbake the brownies. A toothpick inserted into the center should come out with a few moist crumbs for the best texture.Allow the brownies to cool before slicing so they hold their shape.Store leftovers in an airtight container at room temperature for up to 4–5 days.