Combine the berries, sugar, and lemon juice in a saucepan over medium heat. Stir continuously while the sugar melts and the mixture comes to a boil.
Reduce the heat to medium-low and continue cooking for about 8-10 minutes, until the strawberries are soft. Use a wooden spoon to smash the berries a bit as they are cooking.
Place a fine mesh strainer over a large bowl and carefully pour the hot mixture through the sieve. Press down on the cooked berries in the strainer with a wooden spoon to extract as much of the sauce as possible.
Cool completely before transferring the sauce to an airtight container and storing it in the refrigerator.
Notes
If you choose not to strain the sauce, you’ll have made a strawberry compote instead. Both are great options; it simply depends on how you wish to use the sauce.