Beat butter and sugar until pale and creamy. Add eggs, one at a time, beating well after each. Stir in baking soda and grated peel. Fold in half the flour, then half the buttermilk. Repeat. Fold in chocolate chips.
Scoop 1/4 cup batter into prepared muffin tins.
Bake at 375 degrees for 20-25 minutes. Remove from oven.
Brush lemon juice over hot muffins until used up. Sprinkle with sugar. Let stand 5 minutes before removing from pans.