Preheat the oven to 350ºF (180ºC). Grease and flour a bundtlette pan with six 1-cup servings. Make sure to thoroughly grease and flour all of the crevices. (To find the pan I used, see note below.*)
In a medium-sized bowl, whisk together the flour, baking powder, baking soda and salt until well blended.
In a large bowl whisk together the sugar and lemon zest until well combined. Add the oil, eggs, and vanilla extract and whisk until smooth and creamy.
In a small bowl, whisk together the milk and sour cream. Stir the flour mixture into the batter in 2 additions, followed by half of the milk mixture after each addition. Stir just until combined.
Fill the cake pan wells half full with the batter. (If using a standard muffin pan, fill the wells 2/3 full.) Bake until the tops are springy and a toothpick inserted in the centers of the cakes comes out clean or with a few crumbs attached, about 14-16 minutes. Check for doneness a couple of minutes early to avoid over baking. (Baking time is shorter for a standard muffin pan.) Cool the cakes in the pan for 8 minutes, then turn the cakes out onto a cooling rack. Brush the warm cakes generously with lemon simple syrup.