Step 1

Preheat oven to 350F and line an 8×8-inch pan with aluminum foil, spray with cooking spray; set aside.

Step 2

To a large bowl, add the butter, 1 cup flour, 1/2 cup sugar, and optional salt. Using two forks or a pastry cutter, cut butter into dry ingredients until a sandy mixture with peas-sized buttery bits forms.

Step 3

Reserve 3/4 cup of this mixture; set aside.

Step 4

Transfer remaining mixture into prepared pan and using your fingertips or the back of a spatula, lightly press crumbs evenly into pan to form a crust.

Step 5

Bake for 10 minutes. While crust bakes, make the filling.

Step 6

In a large bowl (same one used to make the crust mixture is fine) add the egg, 1/2 cup sugar, sour cream, vanilla extract, 1/4 cup flour, and whisk until smooth; set aside.

Step 7

Remove crust from oven and top evenly with pineapple chunks. About 90% of the surface area will be covered with pineapple; chunks will be very close to each other but not quite touching.

Step 8

Carefully and evenly pour the sour cream mixture over the pineapple, making sure to get it into the corners.

Step 9

Evenly sprinkle the reserved crust mixture over the top to create the crumble topping.

Step 10

Bake for about 35 minutes, or until edges and top are set.

Step 11

Place pan on top of a wire rack and allow bars to cool for at least 1 hour before slicing and serving.