Preheat and Prep: Preheat your oven to 350°F (175°C). Line a 1-pound loaf pan with parchment paper. Set aside. (WATCH VIDEO BELOW)
Infuse the Sugar: In a large bowl, combine the granulated sugar and lemon zest. Use your fingertips to rub them together for about a minute — the sugar will turn pale yellow and smell amazing. This step releases the oils from the zest and makes the whole loaf more lemony.
Mix the Wet Ingredients: Add the melted salted butter to the lemon sugar and mix well. Stir in the vanilla bean paste, then add the eggs one at a time, mixing well between each addition.
Add the Rest of the Wet Ingredients: Add the sour cream, sparkling water, and lemon juice. Mix to combine. Don't worry about stirring out all the bubbles from the sparkling water — they're doing a job!
Fold in the Dry Ingredients: Add the flour, baking powder, and salt. Mix until the batter is smooth and no lumps remain. Do not overmix — stop as soon as it comes together.
Bake: Pour the batter into your prepared loaf pan. Bake at 350°F for 45 minutes to 1 hour, or until a knife or skewer inserted into the center comes out mostly clean. Every oven is a little different, so start checking at 45 minutes.
Make the Vanilla Bean Glaze: While the loaf cools, whisk together all the glaze ingredients in a small bowl until smooth. If it's too thick to pour, add a teaspoon of milk at a time until it reaches a drizzleable consistency. You want it thick enough to coat the top but loose enough to drip down the sides.
Glaze and Serve: Once the bread is fully cool (don't rush this — a warm loaf will absorb the glaze instead of letting it set), remove it from the pan and pour the glaze over the top. Let it drip naturally down the sides. Give it a few minutes to set before slicing.
