Preheat oven to 350 degrees F (175 degrees C). Grease a 8x8-inch baking dish.
Combine white chocolate, butter, and lime zest in a saucepan over medium-low heat; cook and stir until completely melted, 5 to 10 minutes. Remove from heat.
Beat egg in a bowl using an electric mixer until thickened and foamy; add white chocolate mixture, sugar, vanilla extract, and lime juice. Mix well. Fold 2/3 cup plus 1 tablespoon flour into mixture until batter is just mixed. Pour batter into the prepared pan.
Bake in the preheated oven until a toothpick inserted in the center comes out clean, 15 to 25 minutes. Cool blondies before cutting into bars.