Preheat the oven to 350°F (177°C). Grease six 6 ounce ramekins with butter or baking spray. Set aside.

Then, use a vegetable peeler to peel the apples. Core the apples and dice them into 1/2-inch cubes. Transfer the cubed apples to a large mixing bowl.

Add the brown sugar, cornstarch, lemon zest, lemon juice, vanilla extract, cinnamon, apple pie spice, cardamom, and salt. Toss until the apples are well-coated in the spices and the sugar and cornstarch have dissolved. Equally divide the apple mixture between the six prepared ramekins.

To make the topping, combine the all-purpose flour, quick-cooking oats, sugar, brown sugar, cinnamon, and salt in a medium mixing bowl.

Add the melted butter and stir the mixture until it's crumbly and there are no more dry spots. Don't over-mix! Sprinkle the oat topping equally over the ramekins of apple filling.

Place the prepared crumbles on a sheet pan. Bake for 25-30 minutes, until the filling is bubbly and the topping is golden-brown. Let them cool for 5-10 minutes.

Serve the crumbles warm with a scoop of ice cream, a drizzle of caramel sauce, toasted nuts, or other toppings you like. Enjoy!