In a bowl, mix sugar, flour, and baking powder. Cut butter into chunks and add to bowl, along with vanilla. Rub mixture with fingers until it forms coarse crumbs. Then squeeze mixture to make small lumps.
Peel and core quinces and Golden Delicious apples. Cut fruit into 1/3-inch-thick slices and mix in a shallow 2-quart baking dish. Pour sugar-flour lumps evenly over fruit.
Bake in a 350° oven until fruit is very tender when pierced, 55 to 60 minutes. Serve with ice cream.