Sprinkle the yeast in a bowl containing 1/2 cup of lukewarm water and let this sit for a few minutes (till creamy) then stir to dissolve.
Add in 1 cup of the flour, a pinch of salt and stir till you get a soft batter. Cover the bowl with saran wrap and let this sit for about 30 minutes.
Next, stir in the remaining flour, sugar, the lightly beaten eggs, lemon peel, Limoncello and butter. Mix well.
Start kneading the dough by hand for about 5 minutes. The dough should be soft, smooth and just a little bit sticky.
Lightly flour a large bowl and place the dough in the bowl, cover with saran wrap and let the dough rise in a warm draft free place for 1 to 1 1/2 hours. The dough will double in volume.
Transfer the dough to a work surface, lightly press it down with your hands and knead it for about 1 minute.
Divide the dough into 3 equal pieces.
With floured hands, roll each piece of dough out into approximately a 24 inch long rope.
Cut each roll into one inch pieces and place them onto a lightly floured baking sheet.
Pour 2 inches of oil in a medium sized sauce pan or dutch oven and heat to 375* degrees. (use a thermometer)
When the oil has reached 375*, carefully drop in about 6 pieces of dough at a time. (This will also depend on the size of your sauce pan). Don't over crowd them.
When the fritters are golden on one side, flip over to the other side.
Once golden brown on both sides, use a slotted spoon and drain the castagnole on paper towels.
Roll the castagnole in granulated sugar turning to coat all over.
Poke a small hole in the castagnole and use a piping bag fitted with a small round tip and pipe 1/2 to 1 teaspoon of cherry jam into each doughnut.
Serve while still warm, piled high on a serving platter.