Preheat the oven to 200°C. Heat 2 tablespoons of olive oil in a heavy-based roasting pan over medium-high heat. Season lamb and cook for 5 minutes, turning until browned all over.
Roast in oven for 8 – 10 minutes, turning once for medium-rare (or longer, if desired). Rest for 10 minutes covered loosely with foil
Heat the remaining olive oil in a fry pan over medium heat, sauté onion for 5 minutes or until soft. Add cherry tomatoes and pancetta and cook for 5 minutes or until the tomatoes just split
Blanch peas in boiling, salted water for 5 – 7 minutes or until just tender. Drain, add tomato mixture and stir to combine. Season to taste and add mint leaves.
Mint béarnaise
Combine the vinegar, mint sauce, peppercorns and shallot in a small saucepan over medium heat and bring to the boil. Reduce the heat and simmer for 5 minutes or until reduced to 40 ml (2 tablespoons). Strain in a bowl, disregarding the solids
Whisk egg yolks and the vinegar reduction in a large heat-proof bowl over gently simmering water until pale and thick, then gradually whisk in clarified butter until well combined.
Season to taste with sea salt and freshly ground black pepper
Coarsely chop the mint leaves and add to the béarnaise. Stand in a warm place until required. Makes 1 cup.