Line a 9x13 inch baking pan with parchment paper. Cream soft butter and sugar until light and fluffy. Add the lime zest. Beat in the eggs one at a time. Add in the sour cream, and mix until combined.
In a separate bowl, toss the blueberries with 1/4 cup flour (this prevents them from all sinking to the bottom of the cake, thanks Ina!). Combine the remaining flour and baking powder and sift the mixture into the batter as to remove any nasty clumps that could ruin the texture of the cake, and mix just until combined. Gently fold in the berries. *I used the frozen wild blueberries my mom buys in bulk at costco, and took them out of the freezer just before using them so they don't turn the entire cake purple upon defrosting and breaking.
Spread the batter evenly in the pan. Bake at 350 F for 40-45 minutes until a toothpick comes out clean when inserted in the center of the cake. Let cool completely, and dust with confectioner's sugar just before serving, enjoy!