Wash strawberries and remove stems; cut large berries in half or roughly chop them.
Combine strawberries, sugar, and vanilla in a saucepan. Cook over medium-high heat, stirring occasionally. The mixture will sizzle for a while, but then juice will begin to form. Continue stirring; mash a few strawberries with a wooden spoon or heat-proof spatula to help produce the syrup. Cook until sauce thickens, about 15 minutes.
Remove from heat. In a blender, puree about 1/3 of the sauce, then mix back into remaining topping. Store in refrigerator.