Make the apple filling: Choose your apples. You need 5 pounds of apples for this recipe, which is about 9-11 large apples. I like to use a mix of apples for the best flavor, like Granny Smith, Gala, and Golden Delicious.
Use a microplane grater to zest ½ teaspoon lemon peel into a high-sided 12-inch skillet. (SEE NOTE for instructions on how to make this without cooking the apples first; you can skip the skillet and place raw apples directly in the baking dish.) Slice the lemon in half and squeeze the juice into the pan, about 3 tablespoons.
Peel all the apples with a vegetable peeler, or one of those handy apple peelers. Slice the apples very thin, about ⅛ inch, see photos. You should end up with about 9 cups of sliced apples. Add your apples to the skillet with the lemon. Toss the apples with the lemon juice occasionally as you peel, so the apples don't brown.
Cook the apples. (Remember this is optional! See notes!) Once you have all the apples peeled and sliced in the pan, set it over medium heat on the stove.
Add ¾ cups granulated sugar and ¾ cup packed brown sugar over the top of the apples in the pan. Sprinkle 5 tablespoons flour, 1 and ½ teaspoons cinnamon, ¾ teaspoon nutmeg, ¼ or ½ teaspoon cardamom (optional but delicious), and ¼ teaspoon kosher salt on the apples. Stir it together gently so you don’t break all the apples.
Once the mixture is all moistened and you don’t see patches of flour or cinnamon, set a timer for 20 minutes. Cover the mixture with a lid but don’t walk away. Stick around and stir the mixture every 3 minutes or so, replacing the lid each time. Cook for 20 minutes, until the apples are fork tender but still hold their shape. The apples will not soften more while baking in the oven, because of the magic of pectin. So have a taste and see if you want to cook a longer or shorter time. Only you can know your apple al dente perfection level.
Once it's off heat, stir in 1 teaspoon vanilla. Scrape the cooked apples and all the caramel-y-ness into a 9x13 inch casserole dish. Set aside to cool for a couple minutes.
Make the cobbler topping:Preheat your oven to 375 degrees F.
In a large bowl, add the dry ingredients: 2 and ½ cups flour, 1 and ½ cups granulated sugar, 1 teaspoon kosher salt, and 1 teaspoon baking powder. Whisk it together.
In a small bowl, whisk together ½ cup buttermilk* and 1 egg. Pour it into the bowl with the flour, then use a pastry cutter to cut it into the flour, making a shaggy dough. You can use a spoon or fork if you don't have a pastry cutter, be sure to use a cutting motion rather than stirring. It's okay if there are still some dry spots of flour, see photos. Pour or spoon the flour mixture on top of the apples in the 9x13 pan, and spread around evenly.
Chop a stick of butter into ½ inch pieces. Scatter evenly over the top of the flour mixture.
Sprinkle 2 tablespoons sugar over the top. I used half granulated sugar and half demerara (raw) sugar to give it extra crunch.
Bake at 375 for 45-55 minutes. The top should be turning light brown. Once it is light brown all over the top (not just in a few spots) and it's bubbling like crazy, it's done. If you like an extra crispy top, broil the cobbler for 1-3 minutes at this point. No need to move the oven rack up. It gives it an extra crisp browning that I just love. Who doesn't want a crispy crunchy top? But don't walk away! Keep an eye on it, I can't tell you how many things I've lit on fire in my broiler. Check it every 60 seconds.
You are supposed to let it cool completely. Hogwash! Wait 15 minutes to let the juices set up and then dig in! Vanilla ice cream is just not even optional for serving.
Store leftovers loosely covered on the counter; transfer it to the fridge after 2 days.