Pasta Macedonia

Ingredients

• 2 small onions or 1 large, coarsely chopped
• 1/4 pound butter
• 1 pound mezzania, thin tubular pasta, cooked and drained
• 16 ounces sour cream
• 1 1/2 cups crumbled feta cheese
• 12 ripe calamata olives, pitted and sliced
• 1/2 cup finely grated Pardo or Parmesan cheese
• Salt and freshly ground black pepper to taste
• 1 pound fresh spinach, steamed
• Additional feta cheese