Wash the fruit. If needed, trim and slice. The fruit will cook down in the oven, but bite-sized pieces are recommended.
Heat the oven to 350°F. Pull butter out of the fridge and let come to room temperature on the counter while preparing the rest of the crumble.
Using an 8"x8" baking dish, add the fruit. Measure vanilla extract, lemon juice, and lemon zest directly into the baking dish with fruit. Stir to combine.
In a clean bowl, add sugar, corn starch, and pumpkin pie spice. Whisk to combine.
Pour sugar and corn starch mixture over the fruit in the baking dish and mix well. You can use a spatula but I prefer to use my hands. Set aside.
Cut the softened butter into small, manageable chunks using a knife or bench knife. Place in a clean bowl. Add in the flour, oats, and brown sugar. Mix to combine, coating the butter with the dry ingredients and breaking it down into pea-sized pieces. You can use a pastry cutter to do this, which works best. Alternatively, try a hand-held potato masher or just your hands.
Sprinkled the topping evenly onto the fruit in the baking dish.
Bake about 45-55 minutes, until the fruit is bubbling and sticky and the topping is golden brown.
Let the crisp stand for 15-20 minutes before serving. This allows the juices to cool and thicken thanks to the corn starch. Serve with vanilla ice cream.