Start by mincing the shallot and garlic and chopping the basil. Grate the Parmesan fresh if you can. Having everything ready makes mixing quick and keeps the meat cold.
Add the ground chicken, Parmesan, breadcrumbs, shallot, mayonnaise, milk, garlic, basil, lemon juice, salt, and pepper to a large bowl. Use your hands to gently combine everything. Stop as soon as it comes together, because too much mixing makes dense meatballs.
Heat your oven to 375°F. Line a rimmed baking sheet with parchment paper. I use a quarter sheet pan, and it fits twelve meatballs with a little space between them.
Use a 2 tablespoon cookie scoop to portion each meatball. Roll each one lightly between damp hands to smooth the surface. Place them on the pan with a little room between each one.
Bake the meatballs for 15 to 17 minutes until they are golden brown and cooked through. Every oven runs a bit different, so check the first batch early. The meatballs should feel firm and look lightly browned.
For crispy tops, move the pan under the broiler on low for 3 to 4 minutes. Stay close and watch them, because cheese browns fast. This quick step gives the meatballs their golden, crunchy outside.
Let the meatballs rest for about five minutes before serving. They are soft when they come out, and resting helps them firm up. Then serve them with pasta, risotto, or your favorite side.