Grandma Davidson's Baked Apple Pudding

Ingredients:
1 cup packed brown sugar
1 cup all-purpose flour
2 teaspoons baking powder
1/2 teaspoon salt
1/2 teaspoon ground cinnamon
1/2 cup 2% milk
3 medium tart apples, peeled and chopped
2 tablespoons butter, cubed
2 cups boiling water
Vanilla ice cream on the side when serving, optional