Preheat your Oven to 350°F. Lightly Cooking Spray or 6 tbsp unsalted butter cold, cut into small cubes a 9×13-inch Baking Dish (or a 2.5–3 quart Baking Dish) and set aside.

Peel, core, and slice the 3 lb apples peeled, cored, and sliced 1/4-inch thick into uniform 1/4-inch thick slices. Consistent thickness ensures even cooking — too thick and they'll be crunchy, too thin and they'll turn to mush.

Pick your oat type first — it sets your liquid ratio. Rolled oats: 1:2 ratio (e.g., ½ cup oats to 1 cup liquid). Steel-cut oats: 1:3 or 1:4 ratio. Measure liquid into the Pot before adding oats. Use water, milk for creaminess, or stock for savory bowls. Add a pinch of salt to the liquid. No soaking needed for rolled oats; steel-cut can soak overnight to cut cook time, but it's optional.

Bring measured liquid to a boil over medium-high to high heat (lid on speeds this up). Once boiling, diverge by type. Rolled oats: Stir in oats and salt, reduce heat to low, simmer ~5 minutes, stirring occasionally. Done when liquid is mostly absorbed and texture looks soft and cohesive. Still watery? Simmer a few more minutes. Steel-cut oats: Reduce to a gentle simmer, stir in oats, cook 20–25 minutes (Irish-style up to 30), stirring every few minutes. Done when grains are tender with a slight chew. Too thick before fully cooked? Add a splash of water. All types: Keep heat at a gentle simmer after adding oats — no rolling boil. Stir regularly to prevent scorching. If you smell burning, start over; the flavor is already ruined.

Spread the 3 lb apples peeled, cored, and sliced 1/4-inch thick mixture in an even layer in the prepared Baking Dish. Set aside while you make the topping.

In a medium Mixing Bowl, whisk together the 1 cup old-fashioned rolled oats not instant, ¾ cup all-purpose flour, 3 tbsp granulated sugar, 1 tsp ground cinnamon, and ¼ tsp fine salt until combined.

Add the cold 6 tbsp unsalted butter cold, cut into small cubes cubes to the oat mixture. Using your fingertips, work the 6 tbsp unsalted butter cold, cut into small cubes into the dry ingredients by pressing and rubbing until the mixture resembles coarse, clumpy crumbs with some pea-sized pieces of 6 tbsp unsalted butter cold, cut into small cubes remaining.

Pick your oat type first — it sets your liquid ratio. Rolled oats: 1:2 ratio (e.g., ½ cup oats to 1 cup liquid). Steel-cut oats: 1:3 or 1:4 ratio. Measure liquid into the Pot before adding oats. Use water, milk for creaminess, or stock for savory bowls. Add a pinch of salt to the liquid. No soaking needed for rolled oats; steel-cut can soak overnight to cut cook time, but it's optional.

Bring measured liquid to a boil over medium-high to high heat (lid on speeds this up). Once boiling, diverge by type. Rolled oats: Stir in oats and salt, reduce heat to low, simmer ~5 minutes, stirring occasionally. Done when liquid is mostly absorbed and texture looks soft and cohesive. Still watery? Simmer a few more minutes. Steel-cut oats: Reduce to a gentle simmer, stir in oats, cook 20–25 minutes (Irish-style up to 30), stirring every few minutes. Done when grains are tender with a slight chew. Too thick before fully cooked? Add a splash of water. All types: Keep heat at a gentle simmer after adding oats — no rolling boil. Stir regularly to prevent scorching. If you smell burning, start over; the flavor is already ruined.