- Filling:
- 25 large dates, pitted and coarsely chopped
- 1 1/2 cups water
- 6 tablespoons maple syrup
- 2 teaspoons lemon juice
- 1 teaspoon salt
- 1 pinch ground cardamom
- Crust:
- 1 1/2 cups old-fashioned rolled oats
- 1 1/2 cups all-purpose flour
- 1 cup packed brown sugar
- 1 teaspoon baking soda
- 1 teaspoon salt
- 1 teaspoon ground cinnamon
- 3/4 cup cold butter, cubed
- Combine dates, water, maple syrup, lemon juice, salt, and ground cardamom in a non-reactive saucepan over medium heat. Cook, stirring constantly, until dates begin to fall apart, 15 to 20 minutes. Mash the dates with a potato masher into a thick paste. Pour the filling into a bowl; chill in the refrigerator until cool, 30 minutes to overnight.
- Preheat oven to 400 degrees F (200 degrees C).
- Combine oats, flour, brown sugar, baking soda, salt, and ground cinnamon together in a large bowl; add cubed butter. Mix together with your hands until the butter is combined and crust resembles a loose, crumb-like texture. Press 2/3 of the crust into the bottom of a 9×13-inch baking pan. Spread the cooled date mixture on top; cover with remaining crust. Pat lightly to pack together.
- Bake in the preheated oven until topping is lightly browned, 25 to 30 minutes. Cool; cut into squares.