Preheat your oven to 350˚F (175˚C). Spray a loaf pan with baking spray and line with a piece of parchment paper overhanging the long sides of the pan, to use as a sling for removing the cake.
In a large mixing bowl or the bowl of a stand mixer, rub the zest of 1 lemon into 140 g granulated sugar until the sugar resembles damp sand and is very fragrant.
Add 140 g unsalted butter to the mixing bowl and cream together with the lemon-infused sugar until lightened in colour. Use the paddle attachment if you're using a stand mixer.
Add 3 large eggs and 1 large yolk one at a time, beating well after each addition. Add 40 g sour cream, 1 teaspoon vanilla extract, and 1 teaspoon lemon extract and beat well to combine.
In a small mixing bowl, whisk together 140 g all-purpose flour, 1 teaspoon baking powder, and ½ teaspoon fine sea salt. Add to the batter and mix on low speed just until combined.
Pour into the prepared baking pan and smooth out the top. Bake until the top is golden and cracked and a toothpick inserted into the center comes out clean, about 45-55 minutes. Leave to cool in the pan for 5-10 minutes, then transfer to a wire rack to cool completely.
Make the glaze: whisk together 120 g powdered sugar 1 tablespoon lemon juice, and a pinch fine sea salt until smooth. Add more lemon juice a little bit at a time to reach the consistency you want.
Pour the glaze over the top of the cake and let it drip over the sides. Before the glaze sets, sprinkle on some more lemon zest if you like. Let the glaze set for 20-30 minutes, then serve!
