Prep Apples
Grate the peeled apples. Place them in a clean kitchen towel and squeeze firmly to extract as much juice as possible. Crucial Step: Measure out 1/4 cup of this juice and set it aside for the caramel. Discard or drink the rest. You should have about 2 1/2 cups of dry grated apple.

Start Caramel
In a large saucepan over medium heat, bring the granulated sugar (1 1/4 cups), cream of tartar (2 tsp), and the reserved 1/4 cup apple juice to a boil. Stir once to dissolve, then swirl the pan often until the mixture turns a deep amber color (approx. 5–7 minutes).

Season & Cook
Remove from heat. Carefully stir in the small amount of butter (1 1/2 Tbsp), salt, cinnamon, cardamom, and nutmeg. Return to medium-low heat.

Add Apples
Add the dry grated apples. Stir constantly. Note: The caramel may seize up initially this is normal. Keep stirring and cooking until the liquid evaporates and the mixture becomes sticky and clumps together (approx. 9–11 minutes).

Cool
Spread the apple caramel onto a parchment-lined sheet to cool for 30 minutes. Reserve 1/4 cup of this mixture for topping later.

Make Dough
Preheat oven to 375°F (190°C). Whisk flour, salt, baking soda, and cream of tartar in a medium bowl.

Cream Butter
In a mixer with a paddle attachment, beat the chilled butter pieces, granulated sugar, and brown sugar on medium speed until combined (about 2 minutes). Add eggs one at a time, then the vanilla.

Combine
Reduce speed to low. Add dry ingredients and mix until just combined. Add the cooled apple caramel (minus the reserved portion) and pulse a few times to swirl it in. Do not overmix.

Scoop & Top
Scoop dough into balls (about 3 Tbsp each) onto parchment-lined sheets spaced 2 inches apart. Top each cookie with a bit of the reserved apple caramel and a sprinkle of flaky sea salt.

Bake
Bake for 13–16 minutes, rotating pans halfway through. Cookies are done when edges are golden brown. Cool on the sheet for 5 minutes, then transfer to a wire rack.