In a microwave-safe bowl or over a double boiler, melt the butter and ¾ cup of chocolate chips until smooth. Stir occasionally and let cool slightly.

In a large mixing bowl, whisk together the sugar, eggs, and vanilla extract until light and slightly fluffy. Slowly add the melted chocolate mixture, stirring constantly to avoid cooking the eggs.

In a separate bowl, sift together the flour, cocoa powder, and salt. Gently fold the dry mixture into the wet ingredients until just combined. Be careful not to overmix.

Preheat oven to 350°F (175°C). Grease or line a muffin tin or ramekins. Fill each cavity halfway with brownie batter, place a chunk of chocolate or spoonful of ganache in the center, then cover with more batter. Bake for 12–15 minutes until the edges are set but the center is still soft. Let cool for 5 minutes before serving.