Japanese Sweet Potato- Leek Rosti. Spiralize 2 peeled japanese sweet potaoes. Toss with salt, pepper and olive oil. Set aside. Saute one sliced leek with some butter in a nonstick skillet. Add in sweet potatoes. Toss. Add in some fresh thyme leaves if you like. Press down and form into a big "pancake". Saute over medium-high heat for 10 minutes. Flip onto a plate. Heat a bit more butter in the skillet and then slide the pancake back in. Cook for at least another 10 minutes. Slide back onto plate. Top with grated parmesan cheese, a drizzle of olive oil and some chopped fresh parsley.