In a mixing bowl, combine the starter, whole egg, egg yolk and salt. Mix on low speed until the eggs are combined.
With the mixer running slowly add the flour. When the flour has been fully incorporated place the mixer on medium speed and whip for 3 minutes. The batter should be the consistency of thick pancake batter when you are done. Don't overmix.
Cook the Spaetzle
Bring a large pot salted water to a boil. (Use about 2 teaspoons of salt per gallon of water.)
Using the spaetzle making tool of your choice, add batter to the boiling water a little at a time.
Do not put too many noodles through the spaetzle tool at once or they will clump together and get gloppy.
Cook noodles for 2-3 minutes, until they float to the top of the boiling water. (Do not overcooked, or they will get mushy.)
Place cooked noodles in a colander and run them under cold water (or better yet, throw them into an ice water bath) to stop the cooking process.
Set aside and continue process until all noodles are cooked.
Toss cooked rye spaetzle with prepared caramelized cipolini and sauteed mushrooms. Garnish with Tabasco Shallots and arugula, Serve warm.