Prep the pan. Preheat oven to 350°F (175°C). Lightly grease a 24-cup mini muffin tin or line with mini paper liners.
Mix dry ingredients. In a medium bowl, whisk almond flour, cocoa powder, sweetener, baking powder, salt, and espresso powder until no lumps remain.
Whisk wet ingredients. In a separate bowl, whisk eggs, melted butter, vanilla, and almond milk until smooth and glossy.
Combine. Pour wet ingredients into dry. Stir with a spatula just until combined.
The batter should be thick but scoopable. If it’s too thick, add 1–2 teaspoons more almond milk.
Add mix-ins. Fold in sugar-free chocolate chips if using. Don’t overmix.
Fill the cups. Spoon the batter into the mini muffin cups, filling each about 3/4 full.
Smooth the tops with the back of a spoon. Sprinkle a pinch of flaky salt on top if you like.
Bake. Bake for 10–12 minutes, until the tops are set and a toothpick comes out with a few moist crumbs. For fudgy bites, avoid baking until the toothpick is completely clean.
Cool. Let the brownie bites cool in the pan for 10 minutes, then transfer to a rack.
They firm up as they cool.
Serve. Enjoy slightly warm for the gooiest texture, or let them cool completely for cleaner bites.