PREHEAT OVEN TO 425°F. GREASE A 9-INCH BAKING DISH OR SPRINGFORM PAN WITH BUTTER. IF USING SPRINGFORM PAN, WRAP OUTSIDE TIGHTLY WITH FOIL AND PLACE ON BAKING SHEET.
IN A SKILLET, HEAT OLIVE OIL OVER MEDIUM HEAT. ADD PANCETTA AND COOK UNTIL CRISPY, ABOUT 5 MINUTES. REMOVE FROM HEAT.
IN A LARGE BOWL, WHISK TOGETHER THE EGGS, MILK, CREAM, AND SALT AND PEPPER. ADD 2 CUPS OF THE CHEESE, THE SPAGHETTI, AND PANCETTA AND TOSS TO COMBINE.
POUR MIXTURE INTO PREPARED PAN AND TOP WITH REMAINING CHEESE. BAKE UNTIL EGG HAS SET, ABOUT 40 MINUTES.
LET COOL FIVE MINUTES BEFORE CUTTING AROUND SPRINGFORM PAN TO LOOSEN AND RELEASING PAN. SERVE IN WEDGES WITH ADDITIONAL PECORINO AND PARSLEY AND ENJOY!