Finely puree the cooked beetroot in a blender. Beat the eggs in a large bowl with a whisk and add the beetroot puree. Season to taste with nutmeg, salt, pepper and garlic granules.
Cover a deep baking sheet with parchment paper, spread the mixture on it and bake for 15 minutes at 180 ° C. Let cool down.
Turn the sheet of dough out onto aluminum foil or baking paper, carefully peel off the baking paper. Stir the cream cheese until creamy, add the horseradish to taste and brush the beetroot platter with it.
Examine the trout fillets and carefully pull out any bones. Spread the completely boneless fillets on the cream cheese. Roll up the sheet of dough like a Swiss roll and wrap it in foil and put it in a cool place.