Beef and Potato Spanish Tortilla

Ingredients

• 1 recipe Mexican-Style Beef Sausage (recipe follows)
• 2 tablespoons olive oil
• 1-1/2 pounds peeled russet (baking) potatoes, cut in half lengthwise, then crosswise into 1/8-inch slices
• 1 medium onion, thinly sliced
• 6 large eggs, beaten
• 1/2 cup shredded Manchego or Mexican blend cheese (optional)