Warm Strawberry Crumb Cake

Name: Warm Strawberry Crumb Cake
Ingredients: 3 lb strawberries , hulled and halved (8 cups),for filling; 1/2 cup Sugar,for filling; 2 tbsp freshly squeezed lemon juice,for filling; 2 1/2 tbsp cornstarch, dissolved in 2 1/2 tablespoons water,for filling; 1 x vanilla bean split and seeds scraped,for filling; 1/2 cup packed light brown sugar,for crumb topping; 1/2 cup all-purpose flour ,for crumb topping; 2 tbsp all-purpose flour ,for crumb topping; generous pinch of salt,for crumb topping; 4 tbsp Unsalted Butter, cubed and chilled,for crumb topping; 2 1/4 cup all-purpose flour,for cake; 1 tbsp Baking Powder,for cake; 1 tsp Salt,for cake; 1 stick unsalted butter, softened,for cake; 1 1/4 cup Sugar,for cake; 3 x large eggs,for cake; 1 1/2 tsp pure vanilla extract,for cake; 3/4 cup Buttermilk,for cake