Step 1

Preheat oven to 425°F. Place whole grapes in a single layer on a rimmed baking sheet. Sprinkle evenly with sugar, and drizzle with 1/3 cup water. Bake in preheated oven until grapes begin to burst and sugar has dissolved, 15 to 20 minutes, stirring once after 10 minutes.

Step 2

Transfer grape mixture and juices on baking sheet to a food processor; pulse until finely chopped and juicy, about 10 times. Using the back of a spoon, press mixture through a medium wire-mesh strainer into a bowl to yield about 1 1/3 cups grape juice mixture; discard solids. Stir in remaining 1/3 cup water.

Step 3

Stir together grape juice mixture, tequila, lemon juice, and salt in a measuring cup with a spout. If using, place 1 tablespoon grape slices into each of 6 (3.3-ounces) paleta molds. Divide grape juice mixture evenly among molds. Cover with lid, and insert craft sticks. Freeze until firm, at least 8 hours.