Preheat your oven to 350°F and lightly grease a 24-cup mini muffin pan, or line each cup with mini paper liners.

Whisk the melted butter and granulated sugar in a large mixing bowl until smooth. Add the eggs one at a time, mixing thoroughly after each addition. Stir in the vanilla extract, cocoa powder, flour, and salt. Mix until no dry streaks remain.

Fill each muffin cup about two-thirds full with the brownie batter.

Bake for 15 to 18 minutes. Remove from the oven once the tops look set, and a toothpick inserted comes out with a few moist crumbs.

Let the brownie bites cool completely in the pan.

In a separate bowl, beat the softened butter with the brown sugar and granulated sugar until fluffy, about 2 to 3 minutes.

Add the milk and vanilla extract, mixing until smooth.

Gradually add the cooled heat-treated flour until fully incorporated. Gently fold in the mini chocolate chips.

Scoop a portion of dough onto each cooled brownie bite, pressing gently to adhere.

Melt the semi-sweet chocolate chips with the butter or heavy cream in a microwave-safe bowl, stirring until glossy.

Drizzle the melted chocolate over each brownie bite.

Chill in the refrigerator for about 20 minutes before serving.