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 or a potato masher to smash the berries a bit as they cook.

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.