Strawberry Rhubarb Apricot Crisp

For the Filling

• 1 tablespoon softened butter for greasing
• 2 cups thinly sliced rhubarb about 12 ounces
• 2 ½ cups quartered strawberries about 1 lb
• 2 cups apricots pitted and sliced (about 4 medium)
• ¼ teaspoon kosher salt
• ⅓ cup granulated sugar
• 1 tablespoon cornstarch

For the Topping

• ¼ cup granulated sugar
• ¼ cup brown sugar both light or dark work
• ⅛ teaspoon ground cardamom or a generous pinch
• ¼ teaspoon salt
• ½ teaspoon cinnamon
• ¾ cup all purpose flour
• ¾ cup rolled oats
• 8 tablespoons unsalted butter (1 stick), divided
• Vanilla Ice cream or whipped cream for serving, optional