To make the lemon curd (optional):

1. combine all ingredients in a medium saucepan.
2. cook over medium heat, whisking constantly, until the mixture thickens and reaches 175°-180°. DO NOT LET IT BOIL.
3. While still hot, pour the mixture through a strainer.
4. Store in an airtight container in the refrigerator for up to 3 days.

To make the cake:

1. Preheat oven to 350°.
2. Using vegetable oil, grease a loaf pan, then line the bottom with parchment paper.
3. Mix together flour, baking powder and salt in one bowl. Set aside.
4. In a separate bowl, whisk together sour cream, 1 cup sugar, eggs, vanilla, and lemon zest.
5. Combine wet ingredients with dry ingredients.
6. Mix vegetable oil in with a rubber spatula, carefully making sure it's combined.
7. Pour the batter into loaf pan.
8. Add half of the lemon curd (if you are using it, otherwise skip to step 10). 
9. Using a chopstick or a knife, swirl the lemon curd into the cake batter loosely
10. Bake for about 50 minutes (until toothpick comes out clean).

To make the glaze:

1. While cake is baking, mix 1/3 C lemon juice + remaining 1/3 C confectioners' sugar in a small sauce pan until the sugar dissolves. 
2. Set aside.

To glaze the cake:

1. Allow finished cake to cool for at least 10 minutes in the pan before glazing.
2. Carefully remove cake from loaf pan and place on a baking rack or sheet pan.
3. Drizzle the lemon sugar glaze mixture over the cake evenly and allow it to soak in.
4. Slice an serve.