Preheat oven to 400° F and butter a baking dish, something about 8x8 inches, or similar size.
Put the nectarine slices and blueberries in a bowl and gently toss with the sugar, cornstarch and lemon juice. Transfer the fruit into the buttered baking dish.
In a medium sized bowl, whisk to mix the flour, almond flour, sugar, baking powder, and salt. Sprinkle in the butter pieces and use a pastry blender to cut it into the flour—keep going until the lumps of butter are about pea sized. Drizzle in the buttermilk (or milk or cream) and mix with a fork to just combine. Drop in small mounds on top of the fruit.
Bake for 20–25 minutes, until biscuits begin to brown.