Combine strawberries, sugar, and lemon juice in a saucepan. Bring to a boil over medium-high heat, then reduce heat to medium-low and simmer, uncovered, for 15 to 20 minutes, stirring occasionally.

Mash with a fork or potato masher to desired consistency, then simmer 3 to 5 minutes more until the sauce coats the back of a spoon.

Remove from heat and stir in vanilla if using. Let cool in the pan for 5 minutes before spooning warm over desserts.