Preheat your oven to 350°F (175°C). Grease your loaf pan with butter or non-stick spray.
In a large mixing bowl, beat the 2 sticks of unsalted butter and 1 ¾ cups of granulated sugar together on medium speed until light and fluffy, about 3-4 minutes.
Add the 4 extra large eggs, one at a time, mixing well after each addition. Mix in the ¾ cup of freshly grated lemon zest until fully combined.
In a separate bowl, whisk together the 3 cups of all-purpose flour, 1 teaspoon of baking powder, ½ teaspoon of baking soda, and 1 teaspoon of kosher salt.
In another bowl, combine the ½ cup of freshly squeezed lemon juice, ½ cup of buttermilk, and 1 teaspoon of vanilla extract.
Gradually add the dry ingredients to the creamed butter mixture, alternating with the wet ingredients. Mix until just combined; do not overmix.
Pour the batter into the prepared loaf pan and smooth the top. Bake for 55-65 minutes, or until a toothpick inserted in the center comes out clean.
Once baked, let the cake cool in the pan for 10 minutes before transferring it to a cooling rack.
In a medium bowl, whisk together the 2 cups of sifted powdered sugar and 3 tablespoons of freshly squeezed lemon juice until smooth.
Once the cake is completely cool, drizzle the lemon glaze over the top, allowing it to drip down the sides.