Grease an 8 x 4-inch loaf pan and line with parchment paper, set aside.
Pour ½ cup of the cake mix into the bowl of an electric mixer fitted with the paddle attachment (or a hand mixer can be used). Add the butter and mix on medium-low several minutes until light and fluffy.
Add eggs, one at a time and mix until incorporated, scraping the sides of the bowl if necessary. Add the lemon zest and mix 30 seconds.
Add the remaining cake mix alternately with milk, starting and ending with the dry mix. Pour into prepared pan.
Bake for 55-65 minutes or until the cake is golden brown and a toothpick inserted into the center of the cake comes out clean. Cool 10 minutes on a rack. Remove from pan and cool completely.
For the glaze, combine ¼ cup fresh blueberries with 1 tablespoon Blueberry & Lemon Shrub in a small sauce pot with a lid. Cook over low heat until the berries have broken down, about 15 - 20 minutes. Remove from heat.
Place the powdered sugar in a medium bowl and whisk in 1 – 2 tablespoons of the cooked blueberries, using additional shrub if needed to incorporate all the sugar. Use to glaze pound cake, doughnuts, or anything else you want!