Chop a couple tablespoons of the dill and fold through the crème fraiche. Add a little salt and pepper and split the recipe in two. Fold some pouring cream through one of the mixes to make it slightly runny. Place both the mixes in the fridge.
Prepare the rösti: Note: You’ll need a 7.5 cm (3 inch) egg or pastry ring for this recipe. Shred the potatoes on the fine hole processor plate of your food processor or the medium cutting side of your manual grater. Aim for relatively fine strings of potatoes, but not so fine that they become mush. Shred the onion the same way.
Mix the onion and potato in a large mixing bowl. Transfer to a strainer and press out as much liquid as possible. Lay a clean, sturdy tea towel out on your work surface. Transfer half the mix to the center of the tea towel and shape into an oblong shape along the center.
Fold the tea towel around the mix and wring it out over the sink as hard as you can. The aim is to remove as much water in the potato and onion mix as possible. This helps make the finished product crispy. Remove the mix to a large mixing bowl and repeat with the remaining mixture.
Add the egg, chopped dill, and a couple of pinches of salt and pepper. Mix well until combined. Place a large non-stick frying pan over medium-high heat and add a few tablespoons of vegetable oil.
Place the ring in the frying pan and add ½ tablespoon of the potato mix. Using the back of a soup spoon, press the mixture flat and to the edges of the ring, aiming for a thin layer. Remove the ring and repeat the process in another area of the pan.
Once the sides start to brown, turn the rösti over and cook until the other side is browned too. Remove the rösti from the pan and drain excess oil on absorbent kitchen paper for a few minutes. Taste the first few for seasoning and adjust as required.
Once you have mastered the cooking process and are happy with the seasoning, repeat the above process until you have as many as you need. Once drained of all oil, place the rösti on a drying rack set on a flat oven-proof tray.
Five minutes before you’re ready to assemble and serve, place the rack with the rösti into a preheated oven at 180 ℃ (350 ℉).
Cut off any brown unsightly parts of the salmon and then cut it into pieces that will fit well onto the rösti without overwhelming it. Pick off 18-20 sprigs of watercress, rinse and dry them.
Place a small dollop of the thicker crème fraiche mix onto the center of each plate. Use this to glue the first rösti to the plate. Add more of the thick crème fraiche on the rösti; glue a piece of salmon to that, and add a sprig of watercress.
Put a little of the thick crème fraiche on the bottom and top of another rösti, and stack it on the first layer. Repeat the process with another piece of salmon and watercress.
Once the building of each stack is finished, drizzle a little of the runnier crème fraiche around the stack. Serve and enjoy with a chilled Pinot Gris or something fruitier like Chenin Blanc.
