Preheat the oven to 350 F. Line a 12 cup muffin pan with paper liners. In a large bowl, whisk together flour, sugar, cocoa powder, salt, and baking soda. Add in melted butter, eggs, and vanilla extract, and whisk until smooth.
Fold in conversation hearts. Divide the brownie batter between the prepared muffin pan. Bake for 12-15 minutes.