Roast potatoes with gremolata (peeler)

Potatoes

• 1200 g floury potatoes red and blue varieties
• 2 tsp olive oil plus 3 tbsp to roast
• 1200 g water plus extra to parboil
• 1 ½ tsp sea salt plus extra to season
• 3 sprigs fresh rosemary

Parmesan gremolata

• 90 g Parmesan cheese cut into pieces (3 cm)
• 1 ½ garlic cloves
• 3 sprigs fresh flat-leaf parsley leaves only
• 1 ½ lemons peel only, no white pith