Raspberry Peach Crisp

heaping cups diced peach chunks (about 4 medium ripe peaches; I didn’t peel them. Nectarines or mangoes are good subs)

heaping cups raspberries (I used frozen and did not thaw first)

granulated sugar

cornstarch

tablespoons unsalted butter, cold (3/4 of 1 stick)

brown sugar

old-fashioned whole-rolled oats (not quick cook or instant)

all-purpose flour

cinnamon

salt, optional and to taste

whipped cream, whipped topping, or ice cream, optional for serving