I have book of recipes with one for, “Roast leg of Lamb with herbs and a dry sherry/tomato sauce.” The problem is that it dosen’t mention temperature of cooking and I need guidance.
Oven temperature is less critical than you would think. You can successfully roast meat at a surprisingly wide range of temperatures. Say 225ºF to 500ºF.
If you roast it at 350ºF, you'll be fine.
Are you planning on using a thermometer to monitor the roast's degree of doneness?
For a six lb., bone in, leg of lamb, preheat oven to 350' F. Line your roasting pan with aluminum foil, shiny side up. Make a compound butter by combining the herbs and butter together. Place the leg fat-side up on a cooking rack in the roasting pan. Slice shallow, diagonal slits through the fat, to the meat..Rub the compound butter into the slits. Cook to an internal temp of 135' F (about 90 minutes). Remove the roast from the oven to a serving platter. Deglaze the pan with your wine. Pour off liquid into a saucepan. Bring to a simmer.
Combine 1 tbs. cornstarch with 1/4 cup water. Mix to make a smooth slurry. Add that to the pan, whisking as you drizzle it in. When thickened, spread over your roast. Serve with Potato Anna, steak fries, or Hasselback potatoes, and a fresh green salad with Greek salad dressing. You really need to get onboard with using a good meat thermometer. It removes the guesswork from cooking everything from a leg of lamb, to a smoked turkey. Here's a link; https://www.amazon.com/ThermoPro-Wireless-Digital-Cooking-Thermometer/dp/B01GE77QT0