Preheat your oven to 350°F (175°C) and grease an 8×8 inch baking pan.

Melt the butter in a microwave-safe bowl until gooey; let it cool slightly.

In a mixing bowl, combine granulated sugar and brown sugar with melted butter, stirring until well blended.

Add eggs one at a time and mix in vanilla extract until smooth.

In another bowl, whisk together flour, cocoa powder, and salt; gently fold into the wet mixture until just combined.

Pour the batter into the prepared pan, smoothing the top. Bake for 20-25 minutes or until a toothpick comes out with a few crumbs.

Let cool before cutting into heart shapes using cookie cutters.