Apple Crumb Cake

toasted or raw pecans (or nut of your choice)

all-purpose gluten-free flour (I use Better Batter)

xanthan gum (omit if using Better Batter)

granulated sugar, divided

packed brown sugar (any hue will do)

ground cinnamon, divided

kosher salt, divided

unsalted butter, roughly chopped and kept cold

milk (cream is best, low-fat milk is okay)

firm baking apples (like Empire or Granny Smith), peeled, cored & sliced very thin

Bird’s custard powder (or substitute same amount cornstarch)

extra-large egg, plus 1 extra-large egg yolk

pure vanilla extract