Cut one potato into 1.5" / 3.5 cm pieces and cook in boiling salted water for 12-15 minutes or until tender. Drain and mash.
Line a large bowl with a clean linen towel. Using the large holes of a box grater, grate the other potato into the bowl. Squeeze the cloth to extract as much of the starchy liquid as possible. Discard the liquid.
Combine the mashed and grated potatoes, and then stir in the eggs, salt, pepper, and nutmeg. Add the flour, mix well, and pat into small cakes.
In a large skillet over medium heat, melt 2 tbsp. of the butter. Working in batches, cook the potato cakes for 3-4 minutes on each side or until lightly browned and crisp. Transfer the cakes onto a baking sheet and keep warm in a 250°F/130°C oven.
To serve, put a potato cake on each plate and top with a slice of smoked salmon and a dollop of crème fraîche. Garnish with lemon wedges.