Preheat the oven to 375. Line a baking sheet with parchment paper.

Let phyllo sheets defrost in the refrigerator overnight, or let sit on the counter until defrosted, about 1 hour.

Core and thinly slice 3 ½ pounds mixed baking apples about ¼-inch thick. Place apples in a large pot along with 3 tablespoons butter, ⅓ cup lemon juice, ⅓ cup packed brown sugar, 1 ¼ teaspoons ground cinnamon, ¾ teaspoon ground cardamom, and 1 teaspoon salt. Set over medium-high heat and cook, stirring gently from time to time, until the apples soften and the juices cook off, about 12-17 minutes. Sprinkle in 2 tablespoons flour, stir to coat, and set aside. Cool completely.

In a medium bowl, whisk together 3 large eggs, 5 tablespoons melted butter, the remaining 1 cup packed brown sugar, 1 cup light corn syrup, 2 tablespoons vanilla extract, and 1 teaspoon salt, until thick and gooey. Add 2 cups pecans and stir to combine.

Unfurl 1 package phyllo dough. Keep covered with a towel throughout the entire building process. Melt the remaining 8 tablespoons (1 stick) butter. Using a pastry brush, generously coat a 10” cast iron skillet with butter. Working with 1 sheet phyllo dough at a time, drape each one into the skillet, brush generously with butter, and repeat, criss-crossing the sheets. Spoon the apples into the skillet on top of the phyllo and spread into an even layer. Pour the pecan mixture evenly over the apples. Brush 3 more sheets of phyllo with the remaining butter, tear each sheet into 3 pieces, and crumple up to create a raggly, ruffled top crust edge.

Bake on the prepared parchment-lined baking sheet until the phyllo is golden all over, about 1 hour 10 minutes to 2 hours 10 minutes. Let cool. Sprinkle with flaky salt, slice into wedges, and serve, at room temp or slightly warm, with vanilla ice cream.