Preheat your oven to 350F.

Grease an 8×8 inch square cake pan with butter, then line it with parchment paper, leaving some overhang to help you get the cake out later.

Mix together the dry ingredients (flour, salt, baking powder, baking soda) in a bowl and set aside.

To a large mixing bowl, add the sugar and the lemon zest and rub together with your fingers. This helps infuse the sugar with lemon flavor.

Using a whisk or handheld mixer, mix the butter into the sugar and lemon zest.

Mix the milk into the butter and sugar, then mix in the sour cream.

Add the eggs and mix them in until fully incorporated.

Mix in the lemon juice and vanilla.

Mix in the dry ingredients, careful not to overmix.

Pour batter into the cake pan and bake for 30 to 35 minutes or until a toothpick inserted into the center comes out with only a few crumbs. Remove cake from the oven and let it rest for 15 minutes.

Remove the cake from the cake pan and place on a cooling rack to cool completely.

With a handheld mixer, beat together the frosting ingredients until smooth.

Frost the cake, then garnish with more lemon zest, if using.