Preheat oven to 350°F (175°C). Butter and flour** a 9"x 13"x 2" baking pan.
Place the pineapple and blueberries in the pan in a single layer. Sprinkle with sugar and drizzle the vanilla over the top. Gently shake the pan to combine.
To make the topping:
Whisk together the flour, sugar, baking powder, baking soda, cinnamon, and salt.
Sprinkle the topping mixture over the fruit. Gently shake the pan to combine.
Place the cubed butter evenly over the top. Sprinkle the nuts over the top.
Bake 40 to 45 minutes, or until the cake is golden brown and set. The top should spring back with touched.
Notes
*I used fresh pineapple cut into bite-size pieces. If you prefer to use canned, be sure to drain the pineapple before adding it to the pan.
**Alternatively, you can use a cooking spray with flour, like Baker's Joy or Pam for Baking.
To store. After the cake has cooled completely, seal it tightly in an airtight container and refrigerate it for up to 3 days.
To reheat. Reheat servings of blueberry pineapple dump cake briefly in the microwave.
To freeze. You can freeze the cake, although the texture is likely to be affected. Place leftovers in an airtight, freezer-safe container or bag. Properly stored, it should keep in the freezer for about 2 months. Thaw it overnight in the refrigerator before enjoying again.