Preheat the oven to 175°C (350°F) with conventional heat (top and bottom).
Butter the pan and dust it with flour. Tap the pan to remove the excess flour.
In a large mixing bowl, combine the granulated sugar, vanilla sugar, and lemon zest. Rub everything together with your fingertips to release the lemon’s natural oils and infuse the sugar with flavor.
Add the eggs and beat with an hand mixer for about 8 to 10 minutes, starting on medium speed and then increasing to high. The mixture should triple in volume and become pale, thick, and fluffy. This step is very important. You can also use a stand mixer fitted with the whisk attachment.
Once the eggs and sugar are well whipped and fluffy, slowly drizzle in the oil while continuing to beat on medium speed.
Add the milk the same way, then switch to a whisk and gently fold in the sifted baking powder. Fold from bottom to top just until combined, being careful not to deflate the batter.
Sift in the flour in 3 to 4 additions, gently folding with a whisk. Use a bottom to top motion, tapping the whisk against the sides of the bowl occasionally to help the batter pass through the wires. This helps prevent the flour from clumping around the whisk.
If you prefer using a rubber spatula, feel free to do so. The key is to keep the batter light and fluffy without deflating it.
You can also use my second method, which I often use in my crepe recipe to get a perfectly smooth, lump free batter. Rotate the whisk in the center of the bowl to create a gentle whirlpool motion. (Watch the video to see exactly how.).
Once the flour is incorporated, give the batter a few gentle strokes from bottom to top, then a few zigzag motions to smooth it out. The batter should still be light and fluffy. You may even hear a faint airy sound from the bubbles.
Pour the batter into the buttered and floured pan, then bake for about 45 minutes, depending on your oven.
Do not open the oven during the first 40 minutes. Check occasionally through the oven window instead.
Check for doneness by inserting a skewer into the center of the Mouskoutchou. It should come out clean and dry.
Remove from the pan and let it cool on a wire rack.
Once completely cooled, you can dust it with powdered sugar or top it with melted chocolate or jam.