Add the butter and both sugars to a bowl and beat on medium-high for 3 minutes, until noticeably lighter and fluffy. This is key to incorporating air into your batter to get that puff!

Beat in the egg until fully incorporated before mixing in the vanilla and Greek yogurt

In a separate bowl, whisk together the flour, cocoa, baking powder, baking soda, and salt

Mix into the butter mixture until just a few streaks of flour remain

Fold in your milk and mini chocolate chips until combined

Cover the bowl and place in the fridge for 45 minutes

Preheat your toaster oven or regular oven to 400°F for at least 10 minutes. This ensures it’s hot enough before baking. Line your toaster baking tray with parchment paper

On a small plate, sprinkle a layer of extra mini chocolate chips

Scoop a 3 tablespoon-size portion of the chilled dough (don’t flatten!), dip the rounded side in mini chips, and place the flat side on the baking sheet. Place each dough mound at least 2 inches apart on the baking tray. Depending on the size of your toaster, you’ll likely only be able to bake two muffin tops at a time, so cover the rest of the dough and place back in the fridge while the others bake

Bake for 12-14 minutes, rotating your pan if you’re able at the 8-minute mark, until a toothpick inserted into the middle comes out with just a few moist crumbs. Don’t worry if your toothpick has melted chocolate on it. You just don’t want it to be batter

Cool on the baking tray for 5 minutes before moving to a wire rack