Preheat oven to 350° F.
In the bowl of an electric mixer, cream together the butter and sugar for two minutes until fluffy, using the paddle attachment. Stop halfway through to scrape the sides of the bowl with a rubber spatula and return to mixing. Be sure there are no clumps of unmixed butter.
Add the lemon zest and combine.
Add the eggs one at a time, mixing after each addition.
Add the sour cream, lemon juice and vanilla. Mix until combined. (Mixture may separate a bit, but it will come together when flour is added)
Slowly add the flour mixture and mix until just combined. Stop the mixer, scrape the sides and bottom of bowl with a rubber spatula and mix for another 10 seconds. Try to avoid over-mixing.
Grease loaf pans generously with nonstick spray. Spoon batter into pans, filling no more than two-thirds full.
Bake for 45-60 minutes, or until an inserted toothpick comes out mostly clean with only a few crumbs. Mini loaf sizes will need less bake time (closer to 45 minutes). Full size loaves will need more bake time (closer to 60 minutes). All ovens bake differently so be sure to keep an eye on it.
Let bread cool in the pans for 30 minutes before removing and cooling completely on a wire rack.
Prepare the glaze by combining the powdered sugar, milk and lemon zest. Add more powdered sugar or milk to get a thick consistency.
Drizzle over loaves after they have completely cooled. Sprinkle coconut shavings on top before glaze hardens. The glaze should set up and harden in about 30 minutes.