1. Preheat the oven to 350°F. Line a 9 x 9 inch baking pan with parchment paper, allowing the paper to extend over the sides of the pan by 2 inches for easy removal of the cake once baked. Set aside.

2. Add the granulated sugar to a large bowl. Add the lemon zest and use your hands to massage the zest into the sugar for about 20 to 30 seconds. This helps to release the oils from the zest into the sugar which enhances the flavor of the cake once baked.

3. Add the butter and oil to the bowl. Using a hand mixer, or a stand mixer fitted with the paddle attachment, mix on medium speed until light and fluffy, about 2 minutes. Scrape down the sides of the bowl.

4. Add the eggs, one at a time. Mix well after each addition. Scrape down the sides of the bowl as needed.

5. Add the lemon juice and vanilla. Mix on low speed until incorporated. The batter may curdle a bit at this stage. Don’t worry – it will all come back together once the dry ingredients are added.

6. In a separate bowl, whisk together the flour, baking powder, baking soda, salt and poppy seeds. Add the dry ingredients to the butter and egg mixture in three additions, alternating with the sour cream and milk. Begin and end with the dry ingredients. Do not over mix.

7. Transfer the batter to the prepared pan and use an offset spatula to press the batter evenly into the corners of the pan. Level the top. 
8. Bake for 30 to 35 minutes or until the top is golden brown and a toothpick inserted into the center of the cake comes out clean or with a few crumbs remaining. If the cake is browning too quickly towards the end of the baking time, loosely cover the top with a large piece of aluminum foil. Do not over bake or the cake will be dry.
9. Remove the cake from the oven and cool in the pan for 30 to 45 minutes. Use the parchment paper overhang to carefully lift the cake out of the pan and place it on a wire rack. Cool completely before adding the glaze.

Glaze

1. To make the glaze, whisk together the powdered sugar and milk or lemon juice and vanilla (optional) until smooth, but pourable. If the glaze is too thick, add more milk or lemon juice. If too thin, add more powdered sugar.
2. Once the desired consistency is reached, drizzle the glaze over the top of the cooled cake. For best results, let sit for 15 to 20 minutes to set before slicing.