Slow Cooker Triple Berry Crisp

Ingredients (12)

• 1 1/4 cups old-fashioned rolled oats
• 3/4 cup  white whole wheat flour 
• 1/2 cup sliced almonds
• 1/2 teaspoon ground cinnamon
• 1/2 teaspoon kosher salt
• 6 tablespoons unsalted butter
• 1/3 cup pure maple syrup
• 5 cups mixed berries
• 1 tablespoon freshly squeezed lemon juice
• 2 teaspoons pure vanilla extract
• 1/2 to 1 tablespoon cornstarch
• Optional for serving: vanilla ice cream