Preheat oven to 325°F and prepare an 8.5x4" loaf pan with butter and parchment paper.

In a bowl, mix the sugar and lemon zest, rubbing them together for 1-2 minutes until the mixture looks fluffy.

Add the eggs, vanilla, and lemon extract. Whisk using an electric hand mixer or stand mixer for 3-4 minutes until the mixture is very light in color and thick.

In a saucepan, heat the butter, oil, and milk on medium heat until the butter melts and the mixture starts to simmer.

Slowly pour the hot butter mixture into the egg and sugar mixture while continuing to whisk.

Sift the flour, cornstarch, baking powder, baking soda, and salt into the batter. Gently fold with a whisk or rubber spatula until combined.

Add the sour cream and lemon juice, gently folding until combined. Avoid overmixing.

Pour the batter into the prepared loaf pan.

Optional: Add softened butter to a piping bag or Ziploc bag, snip a small hole, and pipe a thin line down the middle of the loaf. This helps control the crack as the cake rises.

Bake for 45-55 minutes, checking at the 45-minute mark with a toothpick. It should come out with moist crumbs attached, not wet batter. Baking time may vary based on your oven and pan.

Let the cake cool for 20 minutes.

Meanwhile, prepare the icing by mixing the ingredients together.

Once the cake has cooled, carefully remove it from the pan. Spread on the lemon icing and garnish with more lemon zest.

Slice and enjoy!