2 tbsp. olive oil
1 large Vidalia onion, halved and sliced thin
Kosher salt and freshly ground pepper
3 matzo sheets
6 large eggs, beaten
2 tbsp. unsalted butter
16 to 20 oz. frozen spinach, defrosted with excess water squeezed out
2/3 cup crumbled feta cheese
Heat oil in large skillet over medium-high heat. Reduce heat to medium; add the onions and cook about 8 to 10 minutes until golden, stirring occasionally to prevent sticking. Season with salt and pepper and move to a bowl with a slotted spoon. Remove the pan from the heat and set aside to use later.
While the onions are cooking, break up the matzos into small/medium intact pieces (not crumbs) and soak in a bowl of cold water for 3 minutes. Drain the matzos well and add them to the eggs. Season with salt and pepper.
Add the butter to the remaining oil in the reserved pan and heat over medium-high heat. Add the matzo/egg mixture and cook, stirring constantly, until the eggs are cooked (about 5 minutes). Stir in the spinach and the cheese and cook until heated through. Divide Matzo Brei on 4 plates and top each with a mound of golden onions.