Melt chopped chocolate and butter in a double boiler or microwave until smooth. Let cool slightly.

In a large bowl, whisk together granulated sugar, brown sugar, and melted chocolate mixture.

Add eggs one at a time, whisking well after each addition. Stir in vanilla extract.

In a separate bowl, whisk together flour, cocoa powder, baking powder, salt, and espresso powder.

Fold dry ingredients into the chocolate mixture until just combined. Fold in chocolate chips.

Cover the dough and refrigerate for at least 2 hours (preferably overnight).

Preheat oven to 350°F (175°C). Line baking sheets with parchment paper.

Scoop chilled dough into 2-tablespoon portions, placing them 2 inches apart.

Bake for 10-12 minutes until edges are set but centers appear slightly underdone.

Immediately sprinkle with flaky sea salt. Let cool on the baking sheet for 5 minutes before transferring to a wire rack.

Preheat oven to 350°F (175°C) and line baking sheets with parchment paper.

In a large bowl, combine brownie mix, oil, eggs, flour, and vanilla. Stir until blended.

Fold in mix-ins of choice.

Drop tablespoon-sized dough portions onto baking sheets.

Bake for 10-12 minutes until edges are set but centers remain soft.

Let cool on baking sheets for 3 minutes before transferring to a wire rack.

Preheat oven to 325°F (165°C). Line mini muffin tins with liners or grease with non-stick spray.

Melt butter, then whisk in sugar until combined.

Add eggs one at a time, whisking well. Stir in vanilla extract.

In a separate bowl, whisk together cocoa powder, flour, and salt.

Fold dry ingredients into wet ingredients until just combined. Stir in ¾ cup of mini chocolate chips.

Fill mini muffin cups about 2/3 full. Sprinkle remaining chocolate chips on top.

Bake for 12-15 minutes until edges are set but centers look slightly underdone.

Let cool in the pan for 10 minutes before transferring to a wire rack.