Step 1: Preheat oven to 375°F (190°C). Lightly butter a 9-inch pie dish or an 8×8 inch baking dish.
Step 2: In a large bowl, combine the pitted fresh cherries with 1/2 cup granulated sugar, cornstarch, lemon juice, almond extract (if using), and a pinch of salt. Toss gently until the cherries are evenly coated.
Step 3: Pour the cherry mixture into the prepared baking dish, spreading it evenly.
Step 4: In a separate medium bowl, prepare the crumble topping. Whisk together the all-purpose flour, rolled oats, almond flour, light brown sugar, 1/4 cup granulated sugar, cinnamon, and 1/2 teaspoon salt.
Step 5: Add the cold, unsalted butter (cut into small cubes) to the dry ingredients. Using your fingertips, a pastry blender, or a fork, cut the butter into the mixture until coarse crumbs form. A few larger pea-sized pieces are fine.
Step 6: Stir in the sliced or slivered almonds until just combined.
Step 7: Evenly sprinkle the crumble topping over the cherry mixture in the baking dish. Do not press down too firmly.
Step 8: Place the baking dish on a rimmed baking sheet and bake for 40-50 minutes, or until the topping is golden brown and the cherry filling is bubbly and thick.
Step 9: Remove from the oven and let it cool on a wire rack for at least 20-30 minutes before serving. This allows the filling to set properly.