Start by cooking the apple filling. Combine diced apples, brown sugar, lemon juice, cornstarch, cinnamon, and nutmeg in a medium saucepan over medium heat. Stir often as the apples soften and the mixture thickens into a cozy, spiced sauce. If it gets too thick before the apples are tender, add water little by little.
Once ready, remove from heat and let it cool completely, this makes filling the cookies much easier.
Preheat your oven to 350°F (160°C fan). Lay parchment paper over a baking sheet and put it aside until needed.
Whisk together flour, baking soda, nutmeg, cinnamon, and salt in a bowl to form a smooth, flavorful starting point for your dough.
Beat softened butter with brown and granulated sugars in a big bowl until the mixture becomes airy and creamy. Add the egg and vanilla, mixing until smooth.
Gradually add the dry ingredients to the wet, mixing gently until you have a soft, slightly sticky dough.
Scoop out about 2 tablespoons of dough for each cookie, placing them on the baking sheet about 2 inches apart.
Bake for 6 minutes, this sets the dough just enough for the filling.
Remove the cookies, press a shallow well in the center of each, then spoon about 3 teaspoons of cooled apple filling into each well.
Return to the oven for 4 more minutes until the edges turn golden and the filling warms through.
Enjoy warm bites of tender cookie filled with spiced apple, pure fall comfort!