Pierce sweet potatoes with a knife or fork a few times. Roast for about an hour at 400F degrees or microwave until fork tender, about 8-10 minutes.
Drain ricotta by squeezing in a with cheese cloth or pressing it in a sieve.
Let them cool and remove the skins.
Chop up the fresh thyme. Mash sweet potatoes in a bowl. Add thyme, parmesan, white pepper, ricotta, 1 egg yolk mix until smooth.
Add 2 cups of flour and mix until incorporated.
If the mixture to too wet add ¼ cup more flour until a desired consistency is reached.
Transfer dough to a a piping bag and cut the tip off so there's a 3/4 inch opening.
Bring a pot of salted water to a boil.
Squeeze gnocchi over the water and cut about 2 inch pieces at a time.
Cook in the boiling water until they float.