Before you start: Peel, core and cut the apples, and keep the topping butter cold. Have the deep baking dish ready and allow the stated 10-minute rest before serving.
Recipe note: Refrigerate perishable leftovers promptly in shallow containers; use within 3–4 days and reheat to 165°F. Count storage from the original cooking date when using leftovers.
Keep the filling and topping measurements separate
Measure the apples after peeling and coring, then keep their pieces within the method's stated thickness as well as its chunk size. Use the filling's flour, brown sugar and cinnamon in the apple bowl. The second flour, sugar and cinnamon amounts belong to the topping, so label the two groups before measuring.
Add the orange zest to the filling with the other listed flavorings. The recipe uses zest rather than an unmeasured pour of orange juice. Spread the prepared apples evenly in the greased deep baking dish before adding the oat topping.
Look beneath the golden oat topping
Keep the butter cold for working through the topping with a fork or pastry cutter. Stir the rolled oats into that crumbly mixture afterward, then scatter it across the filling. This is an oat-topped apple crisp, so an oat-free title or substitution would describe a different recipe.
Check all the signs given in the method: a golden topping, bubbling juices at the edges and an apple piece near the center that admits the knife tip easily. Top color alone can hide apples that need more time. Allow the stated ten-minute rest before dividing the dish into eight dessert portions.
Timing and servings are estimates. Equipment, ingredients and portion sizes affect the result.