Quick and Easy Apple Crisp

Granny Smith Apples, medium size, peeled, cored and sliced (1/4″ thick slices)

granulated sugar

cinnamon

or two of nutmeg (optional)

salt (divided) 

unsalted butter – cold and cut into small pieces

light brown sugar (packed)

all-purpose flour

rolled oats (uncooked)

extra butter to lightly coat baking dish