Wash and dry blackberries. In a large bowl, mix together the blackberries with the 1/4 cup flour, 1/4 cup granulated sugar, lemon zest and lemon juice.
Spread the blackberry filling evenly into an 8 x 8 baking dish.
Crisp Topping
In a microwave safe measuring cup or bowl, melt the butter.
In a clean, large bowl mix together the oats, brown sugar, remaining flour, cinnamon, nutmeg, cardamom and salt.
Add the melted butter and stir together until well combined. Put the bowl in the refrigerator for a couple of minutes to make the topping easier to work with.
Use your hands or a spoon to evenly crumble the oat topping mixture on top of the blackberry filling.
Bake the crisp for about one hour, or until the topping is lightly browned and the filling is bubbling.
Allow to cool, uncovered, on the counter for about one hour before serving.