Preheat the oven to 350°F (175°C) and line a cupcake tin with paper liners. Measure 1 1/2 cups of all-purpose flour and set aside.
Puree fresh watermelon until smooth using a food processor or blender, then strain to remove excess seeds and pulp bits. Measure 1 1/2 cups of watermelon pulp.
1 1/2 cups all-purpose flour
In a large mixing bowl, cream together softened butter and sugar with an electric mixer until light and fluffy, about 3-4 minutes. Observe the mixture become pale and increase in volume.
1 1/2 cups all-purpose flour
Add eggs one at a time, beating well after each addition. The mixture should become smooth and slightly increase in volume. Mix in vanilla extract.
1 1/2 cups all-purpose flour
Alternately add the flour mixture and milk to the wet ingredients, starting and ending with the flour, mixing on low speed. Mix just until combined; do not overmix. Then fold in the watermelon pulp gently until evenly distributed.
1 1/2 cups all-purpose flour
Spoon the batter into cupcake liners, filling each about two-thirds full. Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center comes out clean. Remove from oven and allow to cool on a wire rack.
Prepare the frosting by beating softened butter and powdered sugar together until smooth and fluffy, about 3 minutes. Add a few drops of pink food coloring if desired, and adjust consistency with milk or water to spreadable firmness.
1 1/2 cups all-purpose flour
Once cupcakes are entirely cooled, pipe or spread the pink frosting over each cupcake. Decorate as desired and serve.
1 1/2 cups all-purpose flour
