Preheat oven to 350 degrees F (176 degrees C).
Peel Carrot (2). Remove the outer layer of Onion (1) by removing both ends and then peeling the outside skin. Do not cut the onion in half as it's easier to grate whole. Using the large grate side of the box grater, grate carrot, onion, and Russet Potato (1). Before adding to bowl gently squeeze some of the liquid out.
Add to bowl with 90/10 Lean Ground Beef (1 pound), Italian-Style Breadcrumbs (3/4 cup), Egg (1), Salt (1 1/2 teaspoon) and Ground Black Pepper (1/2 teaspoon) and mix unitl just combined.
Prepare Basmati Rice (1 cup) according to package instructions. I always recommend that you give your rice a quick rinse in a strainer under cold water prior to cooking.
Add Olive Oil (2 tablespoon) to a pan over medium heat. Add meatballs to pan in batches to sear. Turn after 2-3 minutes, or once meatballs are well browned on one side. Leave on the second side for 2-3 minutes, then transfer to a baking sheet.
Once all batches are complete, put the sheet pan in preheated oven for 10 minutes to completely cook through while you make the sauce. Set a timer so they don't turn into hockey pucks in the oven. If you plan to make ahead, skip this last step of finishing the meatballs in the oven. Instead, stop after searing and set aside. See the final instruction step for more details.
Wet a paper towel and ring out well. Wipe Cremini Mushroom (8 ounce) to remove any apparent dirt. Cut into 1/4-inch dice.
In the same pan used for meatballs, add Butter (2 tablespoon). Add diced mushrooms, stir to evenly coat in oil and leave undisturbed for 2-3 minutes. Stir and repeat for another 2-3 minutes or until mushrooms are golden brown and smell nutty.
Add All-Purpose Flour (2 tablespoon) to mushrooms and cook, stirring constantly, for about 2 minutes. You want the flour to smell a bit nutty and to not see any visible white flour anymore.
Add Beef Stock (2 cup) and bring to a boil over medium-high heat. Cook for about 5-7 minutes or until thick enough to coat the back of a wooden spoon. Add the Heavy Cream (2/3 cup) and bring back to a boil. Season with Salt (1/2 teaspoon), Ground Black Pepper (1/2 teaspoon), Garlic Powder (1/2 teaspoon), Onion Powder (1/2 teaspoon) and Worcestershire Sauce (1/2 teaspoon). Cook for another 5 minutes, stirring constantly. Turn off heat.
If you want to make ahead, as noted above, stop cooking meatballs after searing. The meatballs will finish cooking when you reheat them. Cover the bottom of a large casserole dish with the cooked white rice. Top with meatballs and then cover in sauce. Place in the fridge until ready to reheat.
You can serve right off the stove or make this meal ahead. If serving right away, top rice with meatballs that you've finished in the oven, add the sauce, and enjoy!