Preheat the oven to 350°F.
In a medium bowl, toss the strawberries with the corn starch, lemon juice and sugar. Spoon the fruit into four 8-oz oven-safe glass jars, or other similarly sized oven-safe containers. For mine, I like to use actual jam jars.
In another medium bowl, add the flour, baking powder, 1 1/2 tablespoons sugar, and salt, and mix to combine. Add the butter and milk and, using your hands or a fork, stir together to form a dough. Crumble the dough in large pieces over the strawberries, dividing it evenly among the containers.
Brush the tops of the dough with a light coating of egg yolk, and sprinkle about 1/4 teaspoon of the remaining sugar over each jar.
Place the jars on a baking sheet or in a roasting tin to catch any juices that might spill over and bake until the fruit is bubbling and the dough is golden and cooked through, about 25-30 minutes.
The cobblers can be served warm or at room temperature with a scoop of vanilla ice cream on top, if desired.