01 - Preheat oven to 350°F. Line a 12-cup muffin pan with cupcake liners.
02 - In a medium bowl, whisk together the flour, baking powder, and salt until evenly distributed.
03 - In a large bowl, beat the butter and sugar until light and fluffy, approximately 2-3 minutes.
04 - Add eggs one at a time, beating well after each addition. Mix in vanilla extract until fully combined.
05 - Gradually add the flour mixture to the butter mixture, alternating with milk. Begin and end with the flour mixture. Mix until just combined, being careful not to overmix.
06 - Divide batter evenly among the 12 muffin cups, filling each about two-thirds full.
07 - Bake for 16-18 minutes, or until a toothpick inserted in the center comes out clean. Cool cupcakes in pan for 5 minutes, then transfer to a wire rack to cool completely.
08 - Beat the butter until creamy. Gradually add powdered sugar and beat until smooth and well incorporated.
09 - Add watermelon juice, vanilla, and food coloring if using. Beat until light and fluffy, scraping down the sides as needed.
10 - Divide a small portion of frosting and tint it green with food coloring for decorating the edges to mimic the watermelon rind.
11 - Frost cooled cupcakes with the pink watermelon frosting. Garnish with mini chocolate chips to resemble seeds. Optionally, pipe a green ring around the outer edges to create a realistic watermelon appearance.