1. Preheat oven to 350 degrees F and line an 8 x 8 inch square pan with enough parchment paper to create an overhang of at least two inches on two sides.
2. In a medium sized bowl, stir together the flour, baking powder, cardamom and salt. Set aside.
3. In a large bowl, whisk the melted butter with the brown sugar until combined. Add the vanilla, lemon zest and the egg and whisk to combine. With a spatula, fold in the dry ingredients to the wet ingredients and stir until just combined. Gently fold in the blueberries.
4. Pour the batter into the baking pan and smooth the top with an offset spatula.
5. Bake for 30-33 minutes or until a toothpick comes out clean or with just a few crumbs when inserted in the center of the blondies. Place the pan on a wire rack and allow blondies to cool completely in the pan.

FOR THE LEMON ICING

1. In a medium sized bowl, sift the powdered sugar. Add the lemon zest and juice and use a whisk or spoon to combine. Add additional powdered sugar as needed to thicken the icing.