Apple Crisp from cooking class

We made this in cooking class for co-op and it turned out very well.

8 medium apples, peeled/cored/diced
1½ cups packed brown sugar
1 cup all purpose flour
1 cup rolled oats
1½ tsp cinnamon
1½ tsp nutmeg
2/3 cup butter, softened

Preheat oven to 375°.
Put sliced apples into the bottom of a 9x13 lightly greased baking dish.
In a bowl combine brown sugar, flour, oats, cinnamon, nutmeg, and butter.
Mix until combined  well. Spread the mixture over the apples.
Place into the oven and bake for 35 minutes.
If you want to make a smaller amount, half all ingredients and cook in an 8" or 9" dish.