25grams1 oz grated extra mature Wensleydale cheese*
1x tbsp Dijon mustard
2-3tablespoonscold-pressed rapeseed oil
freshly milled salt and black pepper to taste
First, using a a food processor's coarse grating disc, grate both the waxy white and sweet potatoes and place in a large mixing bowl. Cover with cold water and stir thoroughly to get rid of as much starch as possible, then drain in a colander.
Return to bowl, and pour over boiling water. Leave to blanch for 5-6 mins, and drain in the colander.
Pour the grated potato into a clean linen tea towel, wring, and squeeze as much moisture as possible. You may want to have 2-3 goes at this.
Turn the grated potato into the same mixing bowl you used for blanching, then add the grated Wensleydale cheese, 2 tablespoons rapeseed oil, Dijon mustard, and season well. Mix thoroughly.
Line a flat surface with grease-proof paper and grease lightly . Fill a chef's ring with the Rosti mixture, and press down using the plunger so that the mix is as compressed as possible. Repeat until you have made four Rostis.
Heat up to high a griddle pan, and add the remaining tablespoon of rapeseed oil. Carefully slide the Rostis onto the pan, then cook for 5-6 mins until the base starts to brown.
Carefully flip over the Rostis, and continue cooking for a further 5-6 min. Please note: if the Rosti starts to lose its shape, do not worry. They can be reassembled using the chef's ring prior to serving.
Turn onto a plate, and serve piping hot.
Finally, and this is entirely optional.... I quite like a firmer texture of the grated potatoes. Should you want these softer on the inside, transfer onto a baking tray and cook for a further 10-15 minutes at 200C.
* Should a mature Wensleydale cheese be hard to source, a good strong cheddar makes for a good substitute.