Preheat the oven to 175ºC / 350ºF ,and grease and prepare a baking pan. I used a square brownie pan with 19×19 cm / 7,5×7,5 inches dimensions.
For the crumble, start with mixing all the dry ingredients in a bowl. In a separate small bowl, whisk together the sweetener, nut butter and water. Add the wet to the dry and toss/massage to combine.
Transfer 2/3 of the crumble to the baking pan. Using your hands or a spoon press the crumble into a flat layer.
Mix all the ingredients for the caramel smooth in a food processor or mixer. In a bowl, toss the chopped/sliced apple in the cinnamon and cardamom.
Transfer the caramel to the baking pan, smooth out, and top with the apple and the rest of the crumble. Bake for 30-40 minutes until fully baked and golden. Let cool for 10 minutes before slicing up and serving.