On the day, reheat the oven to 180C/Gas 4/fan oven 160C. Heat the olive oil in a frying pan over a medium heat. Tip in the pancetta and fry for 4 minutes until crisp. Drain and cool on kitchen paper.
Whisk the eggs with the cream and plenty of salt and pepper. Add the herbs, parmesan and cooled pancetta; mix again.
Butter a 12-hole muffin tin. Ladle in the mixture to two-thirds fill each hole (you’ll have leftovers for another batch). Bake for 20-25 minutes until firm. Transfer to a rack. Cool while cooking the remaining frittatas. Make up to 4 hours ahead.
To serve, heat through, loosely wrapped in foil, in a preheated oven at 180C/Gas 4/fan oven 160C, for 10-15 minutes. Serve hot, warm or cold.