Mix the yeast, warm milk, one teaspoon of sugar, and one teaspoon of flour . In a small bowl and set aside to activate for 5 minutes.
In a large bowl, combine eggs, the remaining sugar, salt, lemon zest, and ¼ oil. Add yeast mixture and slowly incorporate the flour, until the dough is well combined.
Gently flour your workspace, and knead your dough. Place the dough in a clean bowl, cover with a tea towel, and allow it to rest for 20 minutes.
Once the dough is rested, separate it into four sections in order to make it easier to work with and roll the dough out about ¼ inch thick.
Use a medium-diameter glass to cut out circles. Heat about 4 cups of oil (about 3 deep) in a large pan to ~350 degrees.
While the oil is heating, combine vanilla sugar, and powdered sugar in a separate bowl (this is for sprinkling your donuts). Place about 5 donuts in at a time, allowing them to fry for about a minute on each side.
Once the donuts are golden brown, remove and place them on paper towel lined tray. Allow the donuts to cool down for a couple of minutes, and you can either roll them in icing sugar, or use a sieve to sprinkle them lightly.
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