Step 1 Place the potatoes in a small pot and add water to cover. Place the pot over high heat and bring to a boil. Cook the potatoes until tender (a knife will pierce easily), about 15 minutes (time will very depending on size). Drain the water from the pot, and coarsely mash the potatoes. Add 1 tablespoon olive oil and stir until well combined, if slightly lumpy. Place the mashed potatoes in a medium bowl (you should have 1 cup; discard any excess or save for another use). Set aside.
Step 2 Heat a medium skillet over medium heat until hot, then add 1 tablespoon olive oil. Add the chopped onion and garlic and a pinch each of salt and pepper. Saute, stirring frequently, until the onions are soft and translucent and lightly golden, about 5 minutes. Remove the pan from heat and add the onions and garlic to the bowl with the mashed potatoes. Set the pan aside, but don't wipe it out; any excess oil and flavoring will help flavor the cakes.
Step 3To the bowl with the potato and onion mixture, add the rice, egg, flour, nutmeg, green onions and several grinds of pepper, or to taste. Stir to combine, then cover with plastic wrap and refrigerate for 20 minutes to chill.
Step 4In a separate medium bowl, combine the smoked trout, sour cream and horseradish. Stir gently with a fork so the sour cream is evenly distributed and the trout flakes apart (this is also a good time to check for and remove any stray bones). Stir in the lemon juice, Tabasco, dill and salt and pepper to taste. Stir once more to combine, then cover and refrigerate.
Step 5Remove the rice mixture from the refrigerator and shape one-fourth cup portions of the mixture into cakes about 2 1/2 inches in diameter and three-fourths-inch thick. Press each of the cakes firmly when forming to bind it together; the formed cakes will be a bit fragile.
Step 6Place the pan previously used to saute the onions over medium-high heat and add enough oil to form a thin film over the bottom of the pan, about 1 tablespoon. Working in batches so the pan is not crowded, gently saute the cakes until they are crispy and browned, about 3 minutes per side (adjust the heat of the pan as needed so the cakes do not over-color before they cook inside). The cakes will be a bit fragile, so use care when flipping them. Transfer the finished cakes to a paper towel-lined plate and repeat until the cakes are done.
Step 7To serve, place 2 to 3 warm cakes on each plate, topped with a heaping one-fourth cup of the smoked trout spread. Drizzle with lemon juice, a few snips of dill, and salt and pepper to taste.