Preheat the oven to 350°F. Grease and flour a standard loaf pan (see note). Bring cold ingredients to room temperature.
Zest and extract the juice from 3 lemons. Set the juice and zest aside.
In a mixing bowl, whisk together the flour, baking powder, and salt. Set them aside.
In a large bowl, beat the softened butter for 3-4 minutes until smooth. Add in the granulated sugar and lemon zest and cream on medium-high speed for 2-3 minutes until it's light and fluffy.
Beat in the eggs one at a time. Then, mix in the vanilla extract, lemon juice, and sour cream until fully combined. The mixture may start to separate (see note).
Use a wooden spoon to gently mix in the flour mixture in 3 additions, alternating with the buttermilk. Be sure to start and end with the flour mixture. Mix just until all of the ingredients are fully combined.
Pour batter into the prepared pan and bake for 40-45 minutes until the edges are light golden brown and a toothpick inserted into the center comes out with moist crumbs but no liquid batter.
Let the cake cool in the pan for 10-15 minutes before turning it out onto a wire cooling rack to cool completely.
FOR THE SYRUP
In a small bowl, whisk together the powdered sugar and lemon juice until smooth. Use a pastry brush to brush the syrup onto the top and sides of the cake while it's still warm.
FOR THE GLAZE
In a medium bowl, whisk together the powdered sugar, lemon juice, and sour cream until it's smooth with no lumps.
Once the cake is completely cooled, drizzle the glaze over the top of the cake. Garnish with zest or lemon slices if desired. Slice, serve, and enjoy!
Notes
Either a 9x5 or 8x4 loaf pan can be used for this recipe*
The lemon juice may cause the wet ingredients to separate slightly but it will smooth out once the flour and buttermilk are added*
Use fresh lemon juice for the best flavor
Measure the flour accurately with the spoon and level method
Don't overmix the batter - mix gently just until the wet and dry ingredients are combined
For homemade buttermilk, mix 1 cup of milk with 1 tablespoon of lemon juice or vinegar and let it sit for 5-10 minutes until it thickens slightly
Brush the lemon syrup on while the cake is still warm so it can thoroughly absorb into the cake