Wash and slice potatoes into disks about 1/8 inch wide.
In a microwave safe dish, sprinkle potato slices with 1/4 cup water, cover with plastic wrap, and microwave on high for 3-4 minutes.
Remove plastic wrap from bowl and allow potatoes to cool while preparing the next step.
In a sauté pan heat olive oil over a medium-high heat and add onions and garlic.
Cook until slightly brown, about 5 minutes.
Add rosemary, flour, and whisk in milk into the mixture.
The addition of flour will cause the mixture to thicken.
Remove from heat, and allow to cool.
In a 9 x 13 inch baking dish, layer the potato slices, layering them roof shingles, until the pan is filled.
Gently fold in eggs, yogurt and 1/2 cup of the Parmesan cheese into the now cooled onion mixture, combining well, and then pour over the layered potatoes.
Top with remaining 1/2 cup Parmesan cheese, and bake for 40 minutes at 375°.