Preheat oven to 375°F. Peel each apple (or not) using a paring knife or peeler. Cut in half through the stem then cut the halves in half to make quarters. For each quarter, remove the core with a single vertical cut. Cut the slice in half lengthwise, then cut crosswise 2 or 3 times to yield 3 or 4 pieces from each apple eighth. Transfer pieces to a bowl as you go and spritz with lemon juice.

When the apples are prepared, sprinkle ⅓ cup sugar over the apples and stir to combine. Heat 2 tablespoons butter in a 10-inch cast-iron pan, add the apples, and cook for 5 minutes. Sprinkle the starch over the apples; cook, stirring, for a couple more minutes, until juices have thickened. Remove from heat and set aside.

Cut the cold butter into the oats, flour, and ½ cup sugar using a pastry blender or your fingers. Keep mixing until the crisp holds together when you pinch it. Mix in the cinnamon and salt, then crumble over the apples.

Bake for 35–45 minutes, until apples are bubbly and the topping is golden. Serve with a dollop of unsweetened Greek yogurt.