The sauce would normally simmer stove top, covered, at a very low heat for about an hour, then continue cooking uncovered, at a higher heat until the onions are brown and most of the liquid has evaporated. To make it in the Sun Oven I once again focused it in indirect sunlight to keep the temperature around 200ºF until the onions were soft. At this point I uncovered the pot, focused the Sun Oven directly towards the sun, and propped the glass door open to allow the steam to escape. Even with the door open a crack the Sun Oven properly focused reached 350º. It was really hot today, 110º, so that might have played a part.
Here's the recipe, using Marcella's quantities. Next time I'm going to use less fat and less pasta.
Smothered Onions Sauce
2 Tbs butter
2 Tbs olive oil
1 1/2 lbs onions, sliced very thin (I used vidalia)
Black pepper, freshly ground
1/2 cup dry white wine
2 Tbs chopped parsley
1/3 cup freshly grated parmesan cheese
1 to 1 1/2 lbs pasta
Put butter, oil, onions, and some salt in a heavy dark pot. Place covered pot in Sun Oven, focused to keep the temperature at 200º, until the onions are soft, about one hour.
Uncover pot. Focus Sun Oven directly towards sun. Prop open door to allow moisture to escape, and continue cooking until the onions turn a deep, dark gold color.
Add the wine, salt and pepper to taste, stir and continue cooking until the wine evaporates.
Remove from Sun Oven stir in parsley.