Heat lemon juice and white wine vinegar in a non-reactive pan until just boiling.
Melt 125g of butter in a heavy-based pan over low to medium heat.
Blend egg yolks and salt in a food processor until combined.
Gradually add the hot vinegar mixture to the egg yolks with the motor running.
Slowly pour in the melted butter until the sauce thickens.
Stir in orange zest and seasoning, then keep the hollandaise warm.
Fry trout fillets in 25g of butter for 2 to 3 minutes per side until opaque.
Caramelise orange and grapefruit segments in the remaining 25g of butter.
Blanch sliced fennel and shallots in boiling water, then refresh in ice water.
Combine the blanched vegetables, caramelised fruit, and parsley in a bowl.
Whisk olive oil with reserved citrus juices and season to create a dressing.
Plate the salad, top with trout, then drizzle with hollandaise and dressing.