If making your own tartlet shells, roll out dough on a floured surface to 1/4 inch thick. Use a circular cookie cutter to cut circles in the dough. Spray a mini muffin tin with nonstick cooking spray. Layer the dough rounds into each muffin tin, trimming as necessary. Make decorative marks on edges with a fork, if desired. Refrigerate for at least 30 minutes. Bake shells at 375 Fahrenheit for about 15 minutes, until golden brown.
For the Spinach Dip Tarts:
Heat the oil in a large skillet over medium heat. Sauté the onion and garlic for 5 minutes until soft. Add the spinach and stir until heated throughout.
Heat the milk and cream cheese in a medium saucepan over medium heat until the cream cheese is completely melted. Add the spinach mixture, salt, Worcestershire sauce, hot sauce, and Parmesan cheese.