Preheat the oven to 350F/177C convection and grease a donut pan (I did 12 large donut molds and 12 minis)
Place the sugar in the bowl of a stand mixer (or a large bowl) and zest the lemon on top. Use your fingers to rub the sugar with the lemon zest to release the oils.
200 grams (1 cup) granulated sugar, 2 large lemon (or 3 small), zested
Add the cake flour, baking powder and salt and whisk until they're evenly distributed.
210 grams (1 3/4 cups) all-purpose flour, 1 1/2 tsp baking powder, 1/4 tsp fine sea salt
Add the oil and butter to the dry ingredients and beat together until they're combined.
60 mL (1/4 cup) canola oil, 56 grams (1/4 cup/4 Tbsp) unsalted butter
Add the egg and vanilla extract and mix until they're fully combined.
1 large egg, 1 tsp pure vanilla extract
Add the sour cream and turn the mixer to low speed, while streaming the milk in. Scrape the edge of the bowl and mix just until the batter is smooth.
113 grams (1/2 cup) sour cream, 80 mL (1/3 cup) whole milk
Fill each donut mold about 2/3-3/4 full and bake for about 8-11 minutes. They are done when you press on the center and it springs back and the edges are golden brown.
Remove them from the oven and let them cool in the pan for 5 minutes, then move them to a cooling rack. Allow the donuts to cool completely before frosting.