Whisk together the brown sugar, oats, flour, cardamom, and salt.
Add in the cold butter until the mixture resembles coarse crumbs with a few pea-sized pieces of butter remaining.
Chill in the fridge for 15–30 minutes before using.
Preheat the oven to 350 F. Line a baking sheet with parchment paper.
Spread the chilled crisp mixture evenly over the prepared baking sheet.
Bake for approximately. 12-18 minutes, or until golden brown. Watch carefully because the brown sugar can burn. Remove from oven and allow the crisp topping mixture to cool.