1. In a skillet, sauté the leeks in olive oil until tender. Let cool.
2. In a small bowl, mix the cream and bread crumbs, set aside.
3. In a large bowl, mix the turkey, leeks, mustard, cheese, salt, pepper, egg, and bread crumb mixture.
4. Using a small ice cream scoop, shape the mixture into meatballs, using about 15 ml (1 tbsp) of the turkey mixture per meatball. Place on baking sheets.
5. Bake the meatballs in a 400°F (200°C) oven for about 20 minutes or until cooked through and golden, stirring halfway through cooking.
6. Serve with mayonnaise.