Combine melted butter with egg, Greek yogurt, milk, red food color, and vanilla in a large bowl.

Combine flour with sugar, cocoa powder, baking powder, baking soda, and salt. Add the dry ingredients to the wet mixture and stir until just combined.

Heat waffle maker to medium-high. Spray with cooking spray and scoop ½ cup batter in the center. Close the lid and cook waffle until steam no longer escapes and the waffle has set. Carefully remove waffle from the maker and let cool slightly on cooling rack. Repeat with remaining batter.

Serve waffles with whipped cream and powdered sugar or ice cream.