Spread the softened butter in the bottom of an 8 x 8 baking dish. Put a layer of pineapple on top of the butter. Mix together the ¼ cup sweetener and the pineapple extract in a small bowl. Sprinkle that on top of the pineapple.
Add the cake ingredient to a food processor. Process until smooth. Drop by spoonfuls on top of the pineapple. Gently spread to cover all the pineapple.
Bake for 30 minutes until golden brown and slightly firm to the touch. Cool for 20 minutes and then invert onto a serving platter. Store leftovers in the fridge.
Notes
Nutrition: This cake has 12 pieces. Each piece has 5 total carbs and 3 NET carbs. These numbers include the small amount of fresh pineapple. I believe that this can be keto-friendly with these numbers. It is up to you if you want to use the real pineapple. Notes on Sweeteners: