Place Yukon Gold Potato (2) into a medium saucepot with Water (8 cup) and Salt (1 teaspoon). Bring to a boil over high heat.
Reduce heat to medium- low, and cover. Simmer until tender, about 20 minutes.
Using a colander drain the potatoes and place into a medium bowl. Add one ounce of the Butter (2 tablespoon), Garlic (1 clove), Salt (1/4 teaspoon) and Ground Black Pepper (1/4 teaspoon). Mix until well combined.
Meanwhile, remove the stem from the Cremini Mushroom (4 ounce) and discard. Slice the mushrooms into half inch sliced pieces, and set aside.
In a medium sauté pan over medium heat add Extra-Virgin Olive Oil (1/2 tablespoon).
When hot, add the mushrooms and add Salt (1/4 teaspoon) and Ground Black Pepper (1/4 teaspoon). Cook for 3 minutes, stirring occasionally. Remove mushrooms from pan and set aside.
In a small bowl mix together half a cup of water and Beef Bouillon Cube (1).
Using the same sauté pan as the mushrooms, add Extra-Virgin Olive Oil (1/2 tablespoon).
When hot, add the 85/15 Lean Ground Beef (8 ounce), Herbes de Provence (2 teaspoon), Ground Nutmeg (1/2 teaspoon), and Tomato Paste (1 teaspoon). Cook and stir until beef is lightly brown and crumbly, about 10 minutes.
Preheat oven to 350 degrees F (180 degrees C).
Lightly grease a baking dish with Extra-Virgin Olive Oil (1 teaspoon).
In an oven-safe baking dish spread the beef mixture evenly amongst the bottom of the dish. Then, cover evenly with Green Peas (1/2 cup) and mushrooms. Spread only 2 cups of mashed potatoes over peas and mushrooms. Crumble with the remaining Butter (1 1/2 tablespoon).
Place in the oven and bake uncovered for 20 minutes until golden brown.