This was my mom's recipe and it has been a family favorite for decades. The ingredients are all unchanged, but her instructions were quite vague so I wrote them out in more detail as I prepared it.
Parboil the baby carrots: Bring 2 qts. water to a boil. Add carrots. Bring back to boil and boil 5 minutes. Drain under cold water to prevent further softening.
Parcook the mushrooms: Cut in half and microwave in 30-second increments until just getting soft.
Parcook the garlic: Peel or leave in peel (your preference) and microwave in 30-second increments until just getting soft.
Set aside all of the vegetables.
Sauce
Combine all of the ingredients and set aside.
Meatloaf
Mix all of the ingredients in a large bowl.
Shape and put in the center of an 11" x 15" rectangular baking dish.
Cover with foil and cook for 45 minutes.
Remove the foil, pour out the fat, cover the meatloaf with the sauce and put the vegetables around the meatloaf.
Cook uncovered for 30 minutes or until the internal temperature is 155° F to 160° F.