Wash the outside of the watermelon thoroughly under cold running water.
Cut off both ends to create flat stable surfaces. Stand upright.
Slice into rounds exactly 2.5cm thick.
Remove rind from each round by cutting around the edge following the curve of the flesh.
Press star cookie cutter straight down through each round with even pressure. Do not rock or twist.
Push each star up and out of the cutter from the bottom.
Pat each watermelon star dry with paper towels.
Place stars on a lined baking sheet. Cover loosely with cling wrap.
Refrigerate for at least 30 minutes until thoroughly chilled.
Arrange chilled stars on a large flat serving platter.
If using tajín finish, squeeze lime juice over stars and dust with tajín immediately before serving.
If using honey mint finish, drizzle warm honey over stars, scatter torn mint leaves, and squeeze lime juice over everything.
Scatter fresh blueberries and strawberries around the stars on the platter.
Tuck mint sprigs into gaps. Add lime wedges around the edges.
Serve immediately after dressing or within 1 hour if keeping plain and refrigerated.