Preheat the oven to 375 degrees F (190 degrees C). Line two 12-cup muffin tins with paper liners.

Stir flour, sugar, 1 tablespoon lemon zest, baking soda, salt, and nutmeg together in a large bowl.

Whisk buttermilk, oil, eggs, lemon juice, and vanilla extract together in a medium bowl. Stir into the flour mixture until just moistened. Fold in blueberries. Spoon batter into muffin cups, filling them about 3/4 full.

Bake in the preheated oven until tops spring back when lightly pressed, 20 to 25 minutes. Transfer muffins onto a wire rack to cool for about 15 minutes.

Meanwhile, combine confectioners' sugar, butter, hot water, vanilla extract, and remaining zest in a medium bowl. Whisk to combine.

Dip cooled muffin tops in glaze. Cool until glaze firms up, about 10 minutes. Dip muffins a second time.