Hachis Parmentier ~ Shepherd's pie

I debated on making this meal tonight or Friday night, but couldn't resist making it early. For tonight's meal, I made Hachis Parmentier. I am using the roast beef from last nights meal.

Ingredients:
4 portobello mushrooms, stems and gills removed
2 tbsp olive oil
salt and pepper
1 tbsp truffle paste optional
1/2 cup plus 2 tbsp unsalted butter
2 shallots, chopped
1 onion, chopped
4 cups mashed potatoes
2 tbsp devon cream or 45% cream
1 1/4 lbs roast beef (leftover), ground or shredded
breadcrumbs for sprinkling

Preheat oven to 375 degrees F

Slice the mushrooms (leave the caps whole if forming the pie into individual ring molds). In a skillet over medium heat, saute the mushrooms in the olive oil. Season with salt and pepper. Add truffle past, if using. To the same pan, add 1/2 cup of the butter. Saute the shallots and onions until soft; do not allow to color.
In a bowl, combine the mashed potatoes and cream.
Spread the portion of the mushroom-onion mixture in the bottom of an ovenproof baking dish. Spread a layer of the beef and then another layer of the mushroom-onion mix, alternating until all has been used. Top with the potatoes. Sprinkles the breadcrumbs over the top, and dot with the remaining butter. Bake for 20-30 minutes or until heated through and the top is golden.

Note: I will be honest, I didn't use mushrooms as nobody in my family likes them. Plus, I couldn't bring myself to use that much butter. I love French people, but I think they use too much oil and butter at times. What I did use instead of mushrooms was diced up carrots and celery. Added a nice touch. Instead of using 1/2 cup of butter, I sprinkled maybe 1 tbsp over the top. My husband also noted that he thinks I should have added a layer of cheese under the potatoes.