Preheat oven to 350° F. Place the sliced apples in a 9×13 pan. Gently fold in the blackberries and brown sugar.
Melt the butter and place in a large bowl. Add the almond flour, oats, brown sugar, cinnamon, and salt and mix to combine. Sometimes I add a bit more oats if the topping seems thin. Spread evenly over the apples and blackberries.
Place crisp in the oven and bake for 45 minutes, checking then to see if the fruit is bubbling and the topping looks crisp. If not, check every five minutes until done. Remove from oven and let cool on a rack. Serve warm or at room temperature.
Crisp will keep, well-covered in the fridge, for 5 days.