1. Heat a 12-inch cast-iron skillet over medium-high heat 5 minutes. Stir together sour cream and horseradish in a small bowl, and chill until ready to use.
2. Melt butter in skillet over medium-high heat; add potatoes, and cook, turning occasionally, about 10 minutes or until potatoes begin to brown and crisp. Add onions and apples, and cook, stirring occasionally, about 10 minutes or until onions are tender and apples are golden.
3. Add salt and pepper to taste; add ground red pepper. Stir in cream. Cook, without stirring, about 5 minutes or until potatoes are deep golden. Using a metal spatula, gently lift and turn hash. Cook 5 minutes; gently stir in trout and herbs. Remove from heat, and squeeze lemon wedges over hash. Serve immediately with sour cream sauce.