In a large saucepan, add potatoes and enough lightly salted water to cover by about 1 inch. Bring to boiling. Reduce to medium heat. Cover and cook for 12 to 15 minutes or until potatoes are tender. Drain and transfer potatoes to a large bowl. Allow to cool for 5 to 10 minutes. Mash with a potato masher. Stir in buttermilk, butter, 1/4 teaspoon salt, and pepper; cover and keep warm.
While potatoes are cooking, add shallots, garlic, Italian seasoning, Worcestershire sauce, and 1/4 teaspoon salt to food processor. Pulse until everything finely chopped. Transfer to a large bowl; add the chicken and mix well. Shape chicken mixture into about 50 3/4-inch meatballs (the size of a small cherry). Pour 3- to 4-cups water into a deep, wide pot or skillet; bring to a simmer. Add meatballs to skillet or pot and cook for 5 minutes or until no longer pink inside. Remove from water with a slotted spoon and place on a paper towel to drain.
To serve, on a plate spoon in enough mashed potatoes to fill a cloud-shaped cookie cutter; carefully lift cutter. Or, just spoon the mashed potatoes on plate. Assemble the meatball raindrops below the mashed potatoes and use broccoli as trees, if desired.
If you do not want to simmer the meatballs, you can also bake them in a parchment paper-lined shallow baking pan for 10 minutes in a 350 degree F. oven.
You can cook the meatballs ahead of time, and freeze them in a heavy plastic bag for up to 3 months. Thaw in refrigerator and reheat in microwave to use.