In a large sauté pan, over medium heat, add the oil. When hot, add onions, carrots and celery. Season with salt and pepper. Sauté for 2 minutes.
Add the duck to the vegetables, add salt and pepper and sauté for 1 minute
Dust the duck with flour and cook for 2 minutes, stirring constantly
Stir in the tomato paste and cook for 30 minutes
Stir in the red wine and veal reduction. Add bay leaves and thyme. Bring to boil
Reduce the heat to medium-low and simmer for 1 1/2 hours. During the last 30 minutes, add the mushrooms.
Remove from heat and cool
Pour the mixture into a deep 9" oval dish
Place spoonfuls of the sweet potatoes over the meat mixture, dot the top of the potatoes with butter
Place in a 350 degree preheated oven on top of a baking sheet (In case the pie spills over). Cook for 30 minutes or until the potatoes are golden brown
Garnish with parsley when serving