1. Preheat the oven to 350°F and line an 8-inch square baking pan with parchment paper. Lightly grease the parchment.

2. Melt the butter and let it cool for a few minutes until warm, not hot.

3. Whisk the melted butter, granulated sugar, and brown sugar until glossy and smooth.

4. Add the eggs one at a time, whisking well after each addition.

5. Stir in the vanilla extract, red gel food coloring, and white vinegar until the batter turns deep red.

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

7. Fold the dry ingredients into the wet ingredients until just combined.

8. Fold in the semi-sweet chocolate chips.

9. Spread the batter evenly into the prepared pan.

10. Warm the Nutella for 10 to 15 seconds if needed, then spoon it over the batter.

11. Use a knife or skewer to gently swirl the Nutella across the top.

12. Bake for 28 to 34 minutes, until the edges are set and a toothpick inserted near the center comes out with moist crumbs.

13. Cool in the pan for at least 45 minutes before slicing into squares.