In a mixing bowl or using a stand mixer or food processor, combine the melted butter, flour, brown sugar, cinnamon, and salt. Mix until a sandy, crumbly texture is formed. Spread the mixture onto a parchment-lined baking sheet. Cover and refrigerate for a minimum of 20 minutes or up to overnight.

In a medium saucepan over medium heat, combine the diced apples, brown sugar, butter, lemon juice, salt, cardamom, nutmeg, and cinnamon. Cook, stirring occasionally, for 5 to 10 minutes or until the apples have softened slightly and the mixture is bubbling. Transfer the mixture to a ceramic or metal bowl and allow it to cool for approximately 15 minutes.

Preheat your oven to 350°F (175°C).

On a lightly floured work surface, roll out the pie crusts. Using a 3-inch round cutter (or a similarly sized glass or lid), cut circles from the dough. Re-roll scraps as needed to make use of the entire crust.

Gently press each dough circle over the bottom of a small glass or mug to shape it into a shallow cup. Transfer each shaped piece into a paper cupcake liner placed inside a muffin tin. Press lightly so the crust reaches about halfway up the sides.

Spoon a small amount of the cooled apple filling into each prepared crust. Do not overfill. Top generously with the chilled crumble topping.

Place the muffin tins in the preheated oven and bake for approximately 20 minutes, or until the crust edges are golden brown and the topping is crisp and aromatic.

Remove from the oven and allow the cookies to cool in the pan for at least 20 minutes before serving. This resting period allows the filling to set and makes removal easier.