1 1/2 pounds fresh raspberries
1/4 cup white sugar
1 tablespoon water, or as needed for desired viscosity (optional)
2 teaspoons lemon juice, or more to taste
Combine raspberries, sugar, water, and lemon juice in a saucepan over medium heat; cook and stir until raspberries break down, sugar dissolves, and sauce is heated through, 3 to 7 minutes.
Remove from heat and press sauce through a fine-mesh strainer to remove seeds.
Cool to room temperature, cover the bowl with plastic wrap, and refrigerate until chilled, at least 45 minutes.