Preheat the oven to 180°C conventional oven/ 160°C fan-forced (356° Fahrenheit/Gas 4). Grease a round baking dish with butter (alternatively, line a baking dish with baking paper).
Heat half of the olive oil in a large frying pan over medium heat. Add the garlic and stir for 1 minute, then add the spinach. Toss until the spinach wilts. Place the spinach into a strainer and use the back of a ladle to press down to extract as much liquid as possible. Alternatively, squeeze the liquid out with your hands. Discard spinach liquid. Set the spinach aside to cool slightly.
Use a fork to lightly whisk the eggs in a medium-sized bowl until combined. Stir in the breadcrumbs, Parmigiano Reggiano (or Grana Padano), remaining 2 tablespoons of olive oil and season well with salt to taste. Stir in the cooled spinach.
Pour the egg and spinach frittata mixture on the base of the greased baking dish. Evenly scatter the frankfurt pieces and Provoletta cheese over the egg and spinach mixture.
Bake the frittata for 32-35 minutes or until cooked through.
Allow the Baked Spinach and Frankfurt frittata to cool for 5 minutes before serving – buon appetito!