In a medium saucepan, combine chopped strawberries and sugar with a spoon. Let it sit for at least 15 minutes until the water comes out from the strawberries.

Cook strawberry mixture over medium heat until it boils, the strawberry chunks get soft, and the sauce thickens. Turn off the heat and let it cool slightly.

If you plan to unmold the panna cotta onto plates, lightly grease the inside of the glasses with vegetable oil and use a paper towel to wipe out most of the oil, leaving only a light residue. Otherwise, you can leave them uncoated.

In a food processor or blender, blend the strawberry mixture with milk until smooth.

Strain the mixture with a fine sieve or cheesecloth to remove the seeds.

Soak the gelatin sheet in cold water until soft. Set aside.

In a medium saucepan, heat the strained strawberry mixture and heavy cream until simmer (do not boil). Remove from the heat.

Squeeze gelatin to remove any excess water and add it to the pan, stirring constantly until the gelatin is melted. Stir in the vanilla extract.

Pour evenly among the prepared molds. Refrigerate until set for at least 4 hours or overnight.

To remove from the mold, dip the bottom of the mold into a pot of hot water for 5 seconds to loosen the panna cotta. Slide a knife around the edge, then carefully turn it over onto a serving plate.