Preheat oven to 350° F.
In a medium bowl, combine strawberry halves, 1/4 cup granulated sugar, 1 teaspoon vanilla extract, and cornstarch (if using.) Mix gently with a large spoon.
Transfer strawberries to a 9 or 10 inch deep dish pie plate (or similar sized baking pan.)
In a separate bowl, combine 1 cup flour, 1/2 cup granulated sugar, 1/2 cup melted butter, 1 teaspoon baking powder and 1/2 teaspoon vanilla extract. Mix together with a spoon.
Spoon mixture over strawberries using a small cookie scoop or spoon.
Bake at 350° for 30 minutes. Remove from oven and sprinkle with turbinado sugar, then bake for an additional 15-20 minutes, until edges are bubbly and top is golden brown.
Remove from oven and let stand at least 10 minutes before serving.