Preheat the oven to 375ºF/190ºC. Arrange a rack in the top third of the oven (the crisp will brown better here). Lightly grease the bottom and sides of a 12-inch cast iron skillet or 2-quart (2 L) baking dish with oil, cooking spray, or vegan butter.
Toast the butter and pecans. Set a medium bowl aside, big enough to fit the crisp topping. Add the sliced butter to a stainless steel, enameled cast iron, or other light-colored saucepan or skillet (don’t use a dark pan or nonstick). Turn a burner to medium heat and heat the butter. Stir occasionally with a silicone spatula.a. Once melted, foamy, and at a bubble (it should take ~ 3 minutes), cook for another 1 minute, stirring frequently (standing back as needed, as it might sputter). b. Now add the chopped pecans and stir frequently for another 2 minutes. c. Take the pan off the heat and pour into the medium bowl to stop cooking. Set aside to cool a bit while you prep everything else. Peel the apples, then slice into wedges or slices ¼” to ½” thick (.6 to 1.25 cm), cutting around the core (see Note 6). Add apples to a large bowl and cover with the lemon juice. Toss with a spatula or your hands to ensure well-coated (so they don’t brown). Prepare the apple filling. Mix the apple mixture with the remaining filling ingredients: maple syrup, vanilla, cinnamon, ginger, cloves, nutmeg, cardamom if using, flour, and pinch of salt. Mix until well combined. Transfer to the greased skillet or pan, using a silicone spatula to get any residual liquid out of the bowl. Spread the apples out as evenly as possible. Make the crisp topping. Once the butter-pecan mixture has cooled off a bit, add the remaining topping ingredients: flour, oats, salt, cane sugar, maple syrup, flaxseed meal, and cinnamon. Mix together with a fork or your hands until it’s a somewhat sticky, slightly sandy mix.
Use your hands to scatter the crumb topping evenly on top of the apple mixture (I like to vary the size of the clumps). Transfer the pan to the oven and bake uncovered for 35 to 40 minutes, or until the juices on the sides are bubbling, the crisp is golden on top, and the apples are tender when pierced with a fork or knife.
Let rest for at least 20 minutes, ideally 45 minutes, so the apples can set up more.