Step 2
Place apples, brown sugar, granulated sugar, cinnamon, nutmeg, and salt in a large bowl; toss to combine. Let stand until apple release about 1/2 cup liquid, 30 minutes to 1 hour. Drain apple liquid into a small, heavy saucepan. Set drained apples aside. Add butter to the pan, and bring to a boil over medium-high; cook, stirring occasionally until liquid is reduced to about 1/3 cup, 3 to 5 minutes.