Heat the oven to 375 degrees (F).
In a 12-inch cast-iron skillet, melt the butter over medium heat. Add the brown sugar, granulated sugar, lemon juice and flour, and cook until sugars dissolve, about 5 minutes. Add the apples and continue to cook, stirring occasionally, until the apples have slightly softened, 7 to 10 minutes. Stir in the cinnamon, nutmeg, and salt, and remove from the heat.
In a medium bowl, use a fork to mix together the flour, 2 tablespoons of the granulated sugar, the baking powder, and the salt. Gradually pour in the heavy cream, and using the fork, to bring mixture together into a sticky dough. Scatter pieces of the dough over the top of the apple mixture in the skillet.
In a small bowl, stir together the remaining 2 tablespoons granulated sugar and the cinnamon. Brush the top of the dough with the melted butter and sprinkle with the cinnamon-sugar.
Place the skillet on a rimmed baking sheet to catch any drips and bake until top is golden brown and both the filling and the topping are cooked through, about 40 minutes.
Serve warm, preferably with vanilla ice cream.
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