Preheat oven to 375 degrees.
Brown the butter by placing butter pieces in a medium skillet. Melt the butter over medium heat, stirring occasionally. The butter will begin to foam. Stir and wait for the butter to turn a caramel brown color and smells nutty. There may be small brown pieces form on the bottom of the pan. That's ok!
Pour butter into a medium size bowl. Add the vanilla, brown sugar to the brown butter. Stir until smooth
and add the flour, oats, pecans, cinnamon, nutmeg, and salt. Stir until combined. Set aside.
Cut the apples in half from stem to end. Use a melon baller or small spoon to scoop out the apple core and seeds.
Dig deep enough so there is a little room to “stuff” the apples with the filling. Remove the apple stems.
Pour 3/4 cup hot water in baking dish. Arrange the apples in the baking dish with open face sided up. Divide the crumble topping between the apples, pressing it down as you go.
Mix remaining brown sugar and cinnamon, and sprinkle evenly over the apples.
Cover the pan with foil and bake for 20 minutes. Remove the foil and bake for 30 additional minutes or until the apples are soft.
Remove from the oven and serve warm with vanilla ice cream and salted caramel sauce!