In a saucepan over medium heat, add raspberries, sugar, water, and cornstarch. Stir to combine.
Bring to a boil. Reduce heat to medium-low and gently mash the berries with a spoon as your sauce cooks. Cook sauce for 10-12 minutes, or until raspberries have broken down and sauce looks shiny. Remove from heat, add vanilla extract, and stir to combine.
Arrange a fine mesh sieve over a bowl and pour your cooked sauce into the sieve, using a rubber spatula to gently press your sauce through the sieve. You should be left with a paste of mostly seeds - this can be discarded. If desired, rinse sieve and repeat to catch any remaining seeds.
Sauce can be served warm or chilled over cheesecake, pancakes, ice cream, pound cake, and more.
