In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and brown sugar on medium-low speed until fluffy and aerated, four to five minutes.

In a large bowl, whisk together the flour, toasted and untoasted oats, baking powder, and salt to combine. Add the dry ingredients to the mixer bowl with the wet ingredients and pulse the mixer on and off, almost like you’re trying to jump-start a car, so the flour gets gradually incorporated without flying all over your kitchen. When the dry ingredients are mostly combined, mix on low to incorporate them fully. Set aside while you make the filling.

In a small saucepan, melt butter over medium heat. When it begins to foam, cook, whisking frequently and watching carefully so it doesn’t burn, until the butter is brown and smells nice and toasty and the milk solids have browned and settled to the bottom of the pan, about 10 minutes. Immediately remove from the heat and transfer the browned butter to a nonreactive bowl so it doesn’t keep browning from the residual heat of the pan. Let cool to room temperature before using.

In a large bowl, combine the apples, brown sugar, cornstarch, browned butter, ginger, lemon zest, and salt. Mix until a syrup develops from the cornstarch, one to two minutes. (It’s OK if the butter doesn’t fully incorporate.)

Pour the apple filling into the prepared pie dish and then pour all the crumble on top. Spread the crumble over the filling to cover the surface, using your hands to break apart any pieces that seem larger than bite-size.

Pat it down to make sure that any spaces are filled with topping. Cover the crumble with aluminum foil and cut a hole at the center of the foil to let steam escape.

Bake the crumble for 40 minutes, then remove the foil and bake for 10 minutes more, until the topping looks like a golden-baked sugar cookie and the filling is bubbling through the topping and looks jammy.

Remove from the oven and let cool for 10 to 15 minutes before serving.

Serve with a scoop of gelato and some powdered sugar on top, if desired.