01 - Preheat oven to 350°F. Line a 12-cup muffin pan with cupcake liners.
02 - Whisk together flour, baking powder, and salt in a medium bowl.
03 - Beat butter and sugar in a large bowl until light and fluffy, about 2–3 minutes.
04 - Add eggs one at a time, beating well after each addition. Mix in vanilla extract.
05 - Gradually add flour mixture to butter mixture, alternating with milk. Begin and end with flour mixture. Mix until just combined.
06 - Divide batter evenly among muffin cups.
07 - Bake for 16–18 minutes, or until a toothpick inserted in the center comes out clean. Cool in pan for 5 minutes, then transfer to wire rack to cool completely.
08 - Beat butter until creamy. Gradually add powdered sugar and beat until smooth.
09 - Add watermelon juice, vanilla, and food coloring; beat until light and fluffy.
10 - Divide a small portion of frosting and color it green for decorating the edges.
11 - Frost cooled cupcakes with watermelon frosting. Garnish with mini chocolate chips to resemble seeds. Optionally, pipe a green ring around the edges to mimic a watermelon rind.