Place the 600g of diced strawberries in a clean container. Add 120g granulated sugar (or rock sugar) and mix gently to coat the strawberries evenly.

Avoid crushing the strawberries while mixing. Let the mixture rest for 1 hour to release the juices and dissolve the sugar.

Transfer the strawberries and their juices to a nonstick pan. Cook over high heat until the mixture comes to a boil.

Skim off any foam that forms on the surface for a smoother texture.

Once boiling, reduce the heat to medium-low and simmer the mixture. Stir constantly, about 20-30 times per minute, to prevent burning and ensure even cooking.

When the mixture starts to thicken, add 20g of lemon juice and stir to combine. This enhances the flavor and helps preserve the filling.

Continue simmering until the filling reaches your desired consistency. To check, scoop some filling with a spoon: it should fall slowly and mound slightly on the spoon without sliding off quickly.

Let the strawberry filling cool completely before use. Store in an airtight, sterilized container in the refrigerator for up to 2 weeks.