Preheat oven to 300 degrees F. Grease a 9x5-inch or 8x4-inch loaf pan with cooking spray. Set aside.
In a medium bowl, mix together the all-purpose flour, poppy seeds, salt and baking powder. Set aside.
In a small bowl combine the sugar and lime zest. Rub the lime zest and sugar in between your fingers for about 30 seconds; this will make it so the lime zest releases its natural oils.
To the bowl of a stand-up mixer, add the lime zest/sugar mixture and softened butter. With the paddle attachment on the mixer, beat for about 5 minutes, until pale in color. Mix in one egg at a time, being sure each egg is incorporated before adding another. Add the lime juice and vanilla extract.
In a measuring cup, measure out the milk.
Fold flour mixture into butter mixture, alternating with the milk mixture, beginning and ending with the flour. Mix until smooth. Add the blueberries and fold them in until evenly disbursed.
Pour the pound cake batter into the prepared 9x5-inch loaf pan and transfer to the oven to bake for 60 to 65 minutes, until a skewer inserted into the center comes out clean. It might take a bit longer, depending on which pan you’re using. Allow the cake to cool for 5 minutes in the pan and then invert onto a cooling rack.