Wash and cut potatoes into small bite size pieces. For micro potatoes, you should only have to cut the larger potatoes in half.
Place potatoes in a large saucepan, cover potatoes with water and heat on high until water begins to boil.
Lower heat to medium and simmer for approx. 15 mins or until potatoes can be easily pierced with a fork.
Tip potatoes into a colander and allow to drain and cool.
Heat 2 tsp of olive oil in a sauté pan, and add mustard seeds before the oil begins to smoke.
Cover pan and heat mustards seeds until they pop, then toss mustard seeds while they're popping.
Remove from heat once popping stops. Remove from pan, drain on paper towel and set aside.
Add butter and 1 tsp of olive oil to sauté pan and heat until butter is almost melted.
Add pearl onions to pan and sauté on a medium heat. You will have to keep an eye on your onions and adjust heat as appropriate. The liquid should mostly evaporate, but not completely dry out.
Sauté until pearl onions are tender, but still have some crunch, they should be nice and golden, then remove from heat.
Whisk mayo, sherry vinegar and cream together then add mustard seeds, and set aside
Tip potatoes into a large mixing bowl, sprinkle alfalfa sprouts over potatoes, and add pearl onions. Mix ingredients thoroughly.
Add mayo dressing and carefully combine until all ingredients are covered with dressing.
Add salt and pepper to taste and serve.