Preheat oven to 400 degrees F. Combine the egg in water in a small bowl and set aside.
In a skillet, cook the sliced onions in a bit of butter and olive oil on very low heat until they soften and start to brown. Mix them frequently so they don't burn.
Meanwhile, roll out the pastry with a bit of flour. Brush some of the egg wash over the entire pastry. Spread the spinach and cheeses on top. Sprinkle with salt. Add the caramelized onions and carefully roll it up.
Slice off the edges so you're starting with clean, sharp ends. Slice the pinwheels into 1/2-inch pieces. Lay them on a foil-lined baking sheet sprayed with nonstick cooking spray. Brush the tops with the remaining egg mixture. Bake for 15 minutes or until browned and bubbly.
Let cool for 10 minutes before serving.
by The Savvy Kitchen