To Make the Dough: In the bowl of a stand mixer fitted with the hook attachment, or you can use a mixing bowl to knead by hand, combine the active dry yeast with ¼ cup warm water and 1 teaspoon sugar. Mix and let bloom for 5-10 minutes, until foamy on top.

Add the remaining water, sugar, flour, salt, vanilla, eggs, and lemon zest. Knead on LOW speed for 2 minutes.

Increase speed to Medium to gradually add in the cubed softened butter. Knead for 5-6 minutes, until the dough pulls away from the bowl. The dough will be on the sticky side.

First Rise: Transfer the dough to a very large bowl greased with olive oil. Cover and let rise in a warm environment for 1-2 hours, until doubled in size.

Second Rise: Punch down the dough, cover again with Saran Wrap, and place in the fridge overnight.

Shaping the Doughnuts: The next day, divide the dough out into 15-16 evenly sized pieces.

Cut a bunch of parchment paper square pieces to place the doughnuts on as they rise. The squares should be about 5x5" big.

Roll each dough piece into a tight ball and place on its own parchment square.

Final Rise: Let the doughnuts rise 3-4 hours, until double in size.

Frying the Doughnuts: Heat up 5-6" of frying oil in a saucepan over medium heat to 350F.

Set a bowl of fine granulated cane sugar to the side of your frying pan.

Working in small batches, transfer the doughnuts into the frying oil on their parchment square. Jiggle the parchment out from underneath to remove. Fry the doughnuts about 2-3 minutes, until you see the bottoms are golden. Flip using two forks to fry another minute or so, until golden on the other side.

Immediately roll the doughnuts in the sugar before placing on a wire rack to cool completely.

Once they've cooled at least 20 minutes, you can pipe your favorite fillings inside like the vanilla bean custard and rhubarb strawberry jam.

TIP: Prep this either the night before or a few hours prior to serving the croissants.

In a small bowl, whisk the egg yolks and sugar for 1 minute. Add the cornstarch and salt. Whisk until smooth.

In a saucepan over medium heat, add the milk to heat just until steaming. Remove from heat.

Ladle a few tablespoons of the hot milk into the egg yolks, whisking immediately to help temper the eggs. Continue to gradually whisk in the milk until you’ve used half of the hot milk.

Transfer the tempered egg yolks into the saucepan with the remaining hot milk. Stir over medium heat until thickened, about 3-4 minutes.

Remove from heat to pour into a mixing bowl. Stir in the butter and vanilla until very smooth. Cover with saran wrap and let cool in the fridge at least 2 hours to overnight.