Preheat oven to 350°F. Place 6 ramekins on a foil or parchment-lined baking sheet.
Toss rinsed berries with sugar and cornstarch. Divide berries evenly among the ramekins.
To make the crumble, combine the flour, brown sugar, oats, cinnamon, and salt in a medium bowl. Add the cubed butter and stir (or use your hands) until it forms crumbles.
Top each berry filled ramekin with the crumble mixture. (If you have any leftover crumbles, it freezes incredibly well and gives you a jumpstart the next time you make it).
Bake for 30-35 minutes or until the juices are bubbly and the topping is browned. When the berry crumbles are warm from the oven, I love to serve them with vanilla ice cream.
Notes
Make Ahead Tip: I love to at least double the crumble part of this recipe to use the next time I make crumble. I keep it in the freezer for a quick-to-prep dessert. You can also prepare the unbaked crumble ahead and refrigerate up to 4 hours before baking.