Preheat oven to 350°F. Butter a 9-inch square baking dish (or 8x8-inch ceramic dish). This takes 10 minutes while oven preheats. Checkpoint: Your oven rack is in the center position and oven shows 350°F on the thermometer.

Peel 6 medium Granny Smith apples using a vegetable peeler, working over a bowl to catch juices. This takes about 8–10 minutes. Cut each apple in half, remove the core with a small knife or corer, then slice each half into 1/4-inch thick slices. You should have about 6 cups of apple slices. Checkpoint: Your apple slices are uniform in thickness and you can see the white flesh with no brown spots yet.

In a large mixing bowl, combine 6 cups apple slices with 1/4 cup granulated sugar, 2 tablespoons brown sugar, 1 tablespoon all-purpose flour, 1/2 teaspoon ground cinnamon, 1/4 teaspoon nutmeg, and 1 tablespoon fresh lemon juice. Using a wooden spoon or silicone spatula, toss gently for about 1–2 minutes until every apple slice is lightly coated and the mixture looks slightly wet. The sugar should begin dissolving. Checkpoint: All apple slices are evenly coated and you can see no dry pockets of sugar.

Pour the apple mixture into your prepared baking dish in an even layer, including all juices from the bowl. Spread the apples with a spatula so they sit in a single layer. This takes 1–2 minutes. Checkpoint: The apple layer is flat and fills the entire bottom of the dish with no gaps.

In a separate medium mixing bowl, whisk together 1 cup old-fashioned rolled oats, 3/4 cup all-purpose flour, 1/2 cup packed brown sugar, 1/2 teaspoon ground cinnamon, and 1/4 teaspoon salt. Whisk for about 30 seconds until combined. No lumps of brown sugar should remain. Checkpoint: The dry mixture is uniform in color with no visible clumps.

Cut 6 tablespoons of cold unsalted butter into small cubes (about the size of peas). Add the butter cubes to the dry oat mixture. Using your fingertips, rub the butter into the mixture for about 2–3 minutes, working quickly so the butter stays cold. The mixture should resemble coarse breadcrumbs or sand—some pea-sized pieces of butter should still be visible. Checkpoint: The texture looks like wet sand with no large butter lumps and no powdery dry spots.

Fold in 1/4 cup chopped pecans using a wooden spoon, stirring for about 20 seconds. Drizzle 2 tablespoons honey over the topping and gently stir for another 20 seconds to distribute the honey evenly. The topping should look clumpy and slightly sticky in places. Checkpoint: Pecans and honey are distributed throughout the topping with no dry pockets.

Spread the crumble topping evenly over the apple filling in the baking dish using an offset spatula or your hands. Gently press down with your fingertips so the topping stays somewhat loose (not compacted into a solid layer). The topping should cover all the apples but still look rustic and chunky. This takes 1–2 minutes. Checkpoint: No apple filling is visible through gaps in the topping, but the topping looks loose and crumbly, not dense.

Place the baking dish on the center oven rack. Set a timer for 35 minutes. Bake at 350°F for 35–40 minutes until the topping is deep golden brown and you see apple filling bubbling around the edges of the dish. The topping should smell strongly of cinnamon and caramel. Check at 35 minutes—if the top is pale golden, bake another 5 minutes. Checkpoint: The top is dark golden brown (not burned—should look like golden toast), and you can see small bubbles of apple filling at the edges of the dish.

Remove the baking dish from the oven using oven mitts. Let it cool on a wire rack or on the stovetop for 10 minutes. The apples will continue cooking slightly and the filling will thicken. The crumble will also become crunchier as it cools. Checkpoint: The crumble is cool enough to touch the dish with a bare hand but still warm (at least 140°F inside).

Serve warm with a scoop of vanilla ice cream, dollop of whipped cream, or a drizzle of caramel sauce. The crumble is best eaten within 2 hours of baking while the topping is at its crunchiest.