Portuguese Coconut Custard Tarts

Ingredients ▢Nonstick vegetable spray oil, (optional) ▢2 tablespoons cornstarch ▢1 cup milk ▢1 cup sweetened shredded coconut ▢3 large eggs ▢1 cup granulated sugar ▢2 tablespoons (1 oz) melted unsalted butter ▢1/4 teaspoon lemon extract ▢pinch of salt