Add the strawberries to a blender and blend until completely smooth.
Strain the strawberry puree through a fine-mesh strainer to remove the seeds. Reserve some of the puree for the strawberry topping.
Pour a small portion of the cold milk into a bowl. Sprinkle the gelatin evenly over the milk and let it sit until softened.
Add the remaining milk, heavy cream, sugar, and vanilla extract to a saucepan. Warm gently over medium-low heat, whisking until the sugar dissolves. Do not let the mixture boil.
Add the bloomed gelatin to the warm cream mixture and whisk until completely dissolved and smooth.
Add the strawberry puree for the panna cotta base and whisk until evenly combined.
Divide the mixture between 6 small serving glasses or jars. Refrigerate for at least 4 hours, or until fully set.
To make the strawberry topping, add the reserved strawberry puree, sugar, lemon juice, and a pinch of salt to a small saucepan. Cook gently, stirring, until slightly thickened. Remove from the heat and let it cool completely.
Spoon the cooled strawberry topping over the set panna cotta and serve chilled.
