We recommend enjoying this crumble with a frothy cappuccino.
Preheat oven to 180°C/350°F. Butter the baking pan and line with parchment paper, letting a couple of inches hang over the sides for easy cake removal from the pan later. Butter the parchment paper lightly, too. To make the crumb topping, whisk together sugar, flour, oats, and salt. Add butter and use your fingers or a food processor to pulse until large clumps form. Refrigerate until ready to use.
To make the strawberry layer, roughly chop strawberries. Combine strawberries, sugar, and flour in a large bowl. Set aside.
For the cake, split and scrape the vanilla bean. Whisk together flour, baking powder, salt, and vanilla bean seeds. In a separate bowl or the bowl of a stand mixer, beat together butter and sugar until light and fluffy. Add the eggs one at a time, beating well after each addition. Stir in flour mixture until combined.
Transfer batter to prepared pan, spread strawberry mixture over it, then top with crumb topping. Bake for approx. 50 min., or until golden and a toothpick inserted in the center comes out clean. Let cool completely before slicing. Enjoy!