Start by preheating your oven to 350°F (175°C). Lightly grease your baking dish with butter or cooking spray. This prevents the apples from sticking to the bottom while they bake into a bubbly sauce.

Peel, core, and slice your apples into thin wedges. Try to keep them all the same size so they cook evenly. Place the slices directly into your prepared baking dish for the next step.

In a small bowl, mix the white sugar, one tablespoon of flour, and cinnamon. Sprinkle this mixture over the apples in the pan. Toss them gently to coat every slice, then pour the water over everything.

In a medium bowl, combine the oats, flour, brown sugar, baking soda, and baking powder. Use a pastry cutter to blend in the cold butter. Work it until the mixture looks like coarse crumbs.

Spread the oat mixture evenly over the top of the apples. Do not press it down too hard. You want it to stay light so the heat can make the topping very crispy and golden.

Place the dish in the oven for about 45 minutes. You will know it is done when the topping is brown. The apple juices should be bubbling up around the edges of the pan.

Remove the crisp from the oven and let it sit for ten minutes. This cooling time allows the sauce to thicken up. It makes serving much easier and keeps the flavors concentrated.