Full-flavored and lean, beef top round roasts lack fat and marbling. This makes these roasts moderately tough, especially when cooked too quickly in a dry heat. Cooking them for hours in a slow cooker causes the collagen in the meat to break down, tenderizing the roast. If you add sauces to the slow cooker that promote the breakdown of collagen, such as tomato sauce or wine, you enhance the tenderness.
Rub oil over the entire roast including the nooks and crannies. This helps to caramelize the exterior of the meat. Season the meat by massaging spices into it. Try using kosher or sea salt, or go for lower-sodium alternatives such as pepper, garlic powder, Italian seasoning paprika, rosemary, thyme and dried onion soup mixes.
Slice the vegetables you are going to use into bite-sized pieces. Common vegetables include onions, carrots, celery, mushrooms and potatoes.
Place the vegetables on the bottom of the slow cooker, if you like your vegetables soft. Set the slow cooker to low heat.
Preheat a skillet over a high temperature. Spread 1 tablespoon of oil over the bottom of the skillet. Place the roast in the skillet. Sear the roast about two minutes on each side, then remove it from the skillet. Searing causes chemical changes in the exterior fibers of the meat called Maillard reactions that enhance the richness and complexity of the flavor.
Place the roast into the slow cooker. Add spices and pour in any liquids called for by your recipe. Liquids used to slow cook roasts include broth, dry wine, cream of mushroom soup, water and even beer and classic cola. Set the temperature to slow heat.
Cover tightly and set on low heat. Allow the roast to cook for 5 to 6 hours. If you are adding vegetables you would prefer to cook for less time, such as baby carrots, zucchini or mushrooms, place them into the liquid around the roast. Replace the lid and let the roast continue to cook for another 1 1/2 to 2 hours.
Check the consistency of the liquid. If you want thicker gravy, remove the meat and vegetables to a serving dish and cover to keep it warm. Pour the liquid into a sauce pan. Heat to a boil. Meanwhile, mix 2 tbsp. of cornstarch with 4 tbsp. of cool water in a small cup. Add the cornstarch mix to the boiling liquid a little at a time, stirring constantly. Continue until the gravy reaches the thickness you desire.