Sauté red onion in enough olive oil to cover bottom of pan until translucent and slightly golden. Add spinach and a pinch of sea salt and toss lightly to coat spinach until spinach is softened and just begins to wilt. Turn off heat and set aside.
Slice yellow onions as thin as possible (or use a mandolin if you have). Sauté w/ ¾ tsp. sea salt over medium high heat in enough olive oil to cover bottom of pan until crisp and deep caramel/mahogany in color (almost on the verge of getting burnt, but not quite).
Take out a muffin tin and place a small portion of the browned yellow onions in each of three or four muffin tins. Press against sides to cover entire bottom and sides of tin. Add a layer of cooked spinach/red onion mixture; smooch out again and add the smoked duck breast (or proscuitto ); pressing against the sides firmly. Crack a quail egg on top of each “nest.”
Bake in 400 degree oven for 7-8 minutes – until whites are cooked and yellows are still golden and silky.
Remove from muffin tins (carefully) using a rounded tablespoon; top with fresh ground black pepper. Serve and enjoy!