This is a kid-friendly brunch dish that can double as a make-ahead, grab and go breakfast that's easy to re-heat (350 oven for 10-12 minutes in foil).
If your corn is still raw, then just pop it into a large pot of salted boiling water for 5 minutes, and then into ice water for 5 minutes. Strip the kernels using a sharp knife, cutting down the length of the cob.
In a deep skillet begin to slowly cook the onions over medium-low heat with the butter. Allow them to become soft and golden (about 25-30 minutes.)
Turn your oven to 375. In a muffin tin, add a dollop of the caramelized onions, a spoonful of the corn kernels, and a spoonful of the grated zucchini. In a separate bowl whisk together the eggs, the milk and a pinch of salt and pepper (and maybe some Harissa or red pepper flakes if you like a bit of heat.) Pour into a bowl with a spout (like a large measuring cup), and pour the egg mixture over top of the fillings, distributing it evenly between all the different muffin tins.
Bake for 25 minutes, until set, with maybe the last minute or two under the broiler. Allow to cool for a few minutes, and slide a skinny spatula around the outside of each egg-muffin. Place a cutting board on top of the muffin sheet pan. With a towel or pot holders, grab the outside edge of the pan and the cutting board together, and all at once flip them over, so the cutting board is now underneath and the muffin tins are upside-down, flush on top of the board.
Either pat the bottom of each muffin tin to release the egg cup, or knock the whole muffin tin and cutting board operation on your countertop gently. Serve warm, and leftovers reheat beautifully for a grab and go savory breakfast during the week.