Preheat Oven: Set your oven to 350°F (175°C). Grease a 9x5-inch loaf pan with butter and sprinkle with flour to prevent sticking.
Mix Dry Ingredients: In a medium bowl, combine 3 cups all-purpose flour, 1 tsp baking powder, and 1/2 tsp salt. Set aside.
Cream Butter and Sugar: Using an electric mixer, beat 1 cup softened butter and 2 cups granulated sugar until light and fluffy, about 3–4 minutes.
Add Eggs: Incorporate 4 large eggs one by one, mixing thoroughly after each, and scrape the bowl’s sides as necessary.
Add Lemon and Vanilla: Mix in 1/4 cup lemon juice, 2 tbsp lemon zest, and 1 tsp vanilla extract.
Combine Wet and Dry: On low speed, add the flour mixture in three batches, alternating with 1 cup buttermilk, starting and ending with flour. Mix until just combined.
Bake: Pour the batter into the pan, level the top, and bake for 55–65 minutes, until a toothpick inserted is clean. Check at 55 minutes.
Cool: Allow the cake to rest in the pan for 10 minutes, then move to a wire rack to cool fully.
Make Glaze: Mix 1 cup powdered sugar and 2 tbsp lemon juice until smooth. Drizzle over the cooled cake.
Set Glaze: Allow the glaze to harden for 15 minutes before cutting.