Preheat your oven to 350°F (175°C) and generously grease a standard loaf pan with butter or non-stick spray.

Cut ripe, seedless watermelon into chunks and place them in a blender. Blend until smooth.

In a large mixing bowl, whisk together the watermelon puree, sugar, melted butter, and eggs (or vegan substitute). Mix until smooth.

In a separate bowl, sift together the all-purpose flour, baking powder, and salt.

Gradually add the dry ingredients to the wet mixture, stirring gently until just combined.

Fold in optional mix-ins like raisins or chocolate chips.

Transfer the batter into the greased loaf pan, smoothing the top.

Bake for 50-60 minutes. Check for doneness by inserting a toothpick into the center.

Once baked, cool the loaf in the pan for 10 minutes, then transfer to a wire rack.