In a medium bowl, combine pineapple, sugar, flour, and cornstarch. Mix until well combined and no lumps remain. Add to casserole dish and spread out evenly.
Spread out dry cake mix over top, spreading out evenly.
Cut butter in pieces and scatter evenly over the top of the cake mix.
Place dish in oven and bake for 45 minutes to 1 hour, or until the top is medium golden brown.
Let cool for at least 10 minutes. Serve with vanilla ice, if desired.