Heat the oven to 350°F (175°C). Grease a 9×5-inch loaf pan with butter and dust it lightly with flour, or line it with parchment paper. In a medium bowl, whisk together the flour, baking soda, and salt. Keep this mixture aside for later.
In a large bowl, beat the softened butter and sugar with an electric mixer until the texture becomes light and airy, about 3–4 minutes.
Add the eggs one at a time, mixing well after each addition. Stir in the lemon zest and 2 tablespoons of lemon juice until fully combined.
Gradually mix in the dry ingredients and buttermilk, alternating between the two and starting and ending with the dry ingredients. Stir gently on low speed until just combined to avoid over mixing.
Transfer the batter into the prepared loaf pan and smooth the surface. Bake for 60–70 minutes, or until a toothpick inserted in the center comes out clean. Let the cake rest in the pan for 10 minutes, and then move it to a wire rack to cool completely.
In a small bowl, combine powdered sugar, lemon juice, and melted butter, whisking until smooth. Add more lemon juice if needed to reach the desired consistency.
Drizzle the glaze over the warm cake and let it sit for 10–15 minutes before cutting and serving.