Preheat oven to 375. In heavy pan, put potatoes and salt with just enough water to cover. Bring to boil over medium high heat. Reduce heat to medium low, cover and simmer til tender, about 20 to 30 minutes.
While potatoes are cooking, in medium skillet, heat canola oil over medium low heat. Add garlic and green onions and saute for 5 minutes. Stir in jalapenos and saute for another 3 minutes. Remove from heat, cover to keep warm, and set aside.
To test potatoes, pierce with a fork. Potatoes should be soft when ready to mash. Drain. Return potatoes to pan and mash with potato masher. Add half and half and butter and beat constnatnly with wooden spoon til potatoes are lighlty and fluffy. Add garlic mixture to mashed jpotatoes. Blend well. Add cheddar cheese, salt, and pepper and blend thoroughly til cheese melts. If mixture seems dry, add a bit more half and half. Transfer to large ceramic ovenproof baking dish. Bake til hot, about 15 minutes.
It's best to serve mashed potatoes right away. To keep mashed potatoes warm on holidays when there are lots of last minute preparations, put them into a slow cooker on low for no more than 30 minutes. Serves 8 to 10