Preheat oven to 325º F. Lightly grease an 11 or 12-inch tart pan with a removable bottom.

For the topping, whisk together flour, brown sugar, cinnamon, and salt in a large bowl. Stir in melted butter and mix until combined and crumbly.

To prepare the cake, whisk together flour, sugar, baking powder, and salt in a large bowl.

In a separate bowl, combine the egg, milk, oil, and vanilla, whisking until well blended.

Add the flour mixture to the egg mixture and stir until just combined. Do not over mix.

Spread the batter over the bottom of the prepared tart pan in a thin, even layer.

Starting from the outside edge and working toward the center, sprinkle the crumb topping evenly over the batter. This will help maintain an even cake layer with topping that reaches all the way to the edge. Gently press the topping into the batter.

Bake until the cake rises and a tester inserted in the center comes out clean, about 40 to 45 minutes,

Remove from the oven and cool slightly before unmolding the cake from the pan. Slice in diamonds or wedges. Serve warm.