FILLING
3 pounds strawberries, hulled and halved (8 cups)
1/2 cup sugar
2 tablespoons freshly squeezed lemon juice
2 1/2 tablespoons cornstarch dissolved in 2 1/2 tablespoons of water
1 vanilla bean, split and seeds scraped
CRUMB TOPPING
1/2 cup lightly packed light brown sugar
1/2 cup plus 2 tablespoons all-purpose flour
Pinch of salt
4 tablespoons unsalted butter, cubed and chilled
CAKE
2 1/4 cups all-purpose flour
1 tablespoon baking powder
3/4 teaspoon salt
1 stick unsalted butter, softened
1 1/4 cups sugar
3 large eggs
1 1/2 teaspoons pure vanilla extract
3/4 cup buttermilk