Make the Cake

1. Prepare the oven at 350°F and meticulously coat a 12-cup Bundt pan with butter and flour, ensuring comprehensive coverage.
2. Combine flour, baking soda, and salt in a medium bowl, whisking thoroughly.
3. Cream butter, sugar, lemon zest, and chopped rosemary using an electric mixer until the mixture becomes airy and voluminous, approximately 3-4 minutes.
4. Incorporate eggs individually into the mixture, beating thoroughly after each addition. Blend in vanilla and lemon juice.
5. Gradually fold in flour mixture and sour cream alternately, starting and concluding with flour, mixing minimally to maintain batter integrity.
6. Transfer batter into prepared Bundt pan, smoothing the surface and gently tapping to eliminate potential air pockets.
7. Bake for 50-60 minutes, covering with foil after 30 minutes if browning occurs rapidly. Verify doneness by inserting a toothpick that emerges with minimal crumbs.
8. Allow cake to rest in pan for 10 minutes before inverting onto a wire rack for complete cooling.

Make the Candied Rosemary

1. Prepare a parchment-lined baking sheet.
2. Whip egg white until frothy and place sugar in a separate container.
3. Delicately brush rosemary sprigs with egg white, then roll in sugar for even coating.
4. Position sugared sprigs on prepared sheet and permit drying for one hour.

Make the Icing

1. Combine confectioners’ sugar, vanilla extract, salt, and water, whisking until smooth.
2. Adjust consistency by incrementally adding water until achieving a thick yet pourable texture.

Assemble the Cake

1. Once cake has thoroughly cooled, drizzle icing across the top, allowing elegant cascading along sides.
2. Permit icing to stabilize for approximately 30 minutes.
3. Garnish with candied rosemary immediately before serving.