Preheat the Oven:
Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

Prepare the Apple Filling:
In a small saucepan, melt 1 tbsp butter over medium heat. Add diced apples, brown sugar, cinnamon, and lemon juice. Cook for 5–7 minutes until apples are soft but not mushy. Set aside to cool.

Make the Cookie Dough:
In a large bowl, cream together softened butter and sugar until light and fluffy. Mix in the egg and vanilla. In a separate bowl, combine flour, baking soda, and salt. Gradually add dry ingredients to the wet mixture until fully incorporated.

Make the Crumb Topping:
In a small bowl, mix flour, brown sugar, and cinnamon. Cut in the cold butter with a fork or pastry cutter until the mixture is crumbly.

Assemble the Cookies:
Scoop cookie dough onto the baking sheet. Slightly flatten each cookie and create a small well in the center using your thumb or spoon. Fill with a spoonful of apple filling and sprinkle generously with crumb topping.

Bake:
Bake for 12–15 minutes or until edges are lightly golden. Let cool on the tray for 5 minutes before transferring to a wire rack.