Begin by preheating your oven to 350 degrees and lining a loaf pan with parchment paper, leaving a little overhang to allow easy removal of the loaf from the pan.
In a large bowl, beat the butter with a mixer for 2-3 minutes until the color of the butter has lightened and it has fluffed up.
Add the rest of the wet ingredients: sour cream, lemon zest, lemon juice, sugar, eggs, milk, vanilla, and vegetable oil. Mix on medium-low speed for 1-2 minutes until well combined. Batter will look wet.
Using a sifter or a fine mesh sieve (see picture above), add the sifted dry ingredients to the wet batter.
Mix the batter on low speed, gradually increasing to medium speed until the batter is well combined. Use a silicone spatula to scrape the bottom, ensuring the the batter is well mixed.
Pour the batter into the prepared loaf ban and place into the oven. Bake for 60-70 minutes (65 is usually perfect for me) until the edges are golden and a toothpick inserted into the middle comes out clean. (It’s okay if there are cracks or if the loaf does not look perfect- the icing will cover it up) Let the loaf cool for about 20 minutes in the pan before removing it from the pan. Place the loaf on a cooling rack and let it sit until completely cooled.
When the loaf has completely cooled, whisk together the icing ingredients. The icing should be kind of thick, but thin enough to spread. Let the icing sit for 10-20 minutes (if you can) to let the icing set before slicing. Enjoy!