Melt the butter in a skillet over medium heat. Add the apples and toss to combine.
Mix in the brown sugar, cinnamon, nutmeg, cloves, ginger, cardamom, and Kosher salt. Bring the apples to a simmer. If you are further baking the apples (like in a pie or cinnamon rolls), simmer the filling just until the apples are slightly softened but still have a bite to them, about 3-4 minutes. If you are using the filling as a topping (like for ice cream or pancakes), simmer the apples until they are completely softened, 5-6 minutes.
Meanwhile, whisk the cornstarch and apple cider (or water) in a small bowl. Add the cornstarch slurry to the apple mixture and stir well. Simmer for another 1-2 minutes, until the filling is thickened and coats the back of a spoon. If it's too thick, add more apple cider or water, 15 grams (1 Tablespoon) at a time, until you reach your desired consistency.
Remove the skillet from the heat and mix in the vanilla extract and apple cider vinegar. Transfer the filling to a bowl or heatproof container and cool completely.