
Over medium heat, sauté chopped onion in olive oil until translucent. Set aside to cool.
Mix spinach, cheeses and eggs in a large bowl. Season with nutmeg, salt and pepper. Add sautéed onions and combine. Set aside.
Spray a 10 to 12 cup bundt pan with cooking spray. Preheat oven to 350 degrees.
Lay phyllo on your work surface. Brush one sheet of phyllo with melted butter. Fold sheet in half, in the width. Place folded phyllo in the bundt pan diagonally, lining the pan, allowing ends to hang over the sides of the pan.
Brush the next sheet with butter and fold as above. Place the second sheet next to first sheet, slightly overlapping, again lining the pan.
Keep brushing, folding and lining the pan until all 10 sheets are used. The entire bundt pan should be lined with phyllo.
Place spinach filling into the lining and fold back overhanging phyllo to cover spinach. Brush top with more melted butter and bake for 60 Minutes. Allow to cool for 10 to 15 minutes and turn out of the bundt.
To prepare this dish in advance, fill pan as directed and freeze it raw. Bake just before serving. You can also bake it in advance and remove from the pan as directed. Refrigerate until needed. Reheat for 15 minutes at 350 degrees.
