Massage the rump steak with cooking oil on both sides, seasoning with salt and black pepper. Sear in a preheated skillet for 4-5 minutes per side, then let rest.

In a large saucepan, bring salted water to a boil. Add rigatoni and cook until al dente (10-12 minutes). Reserve ½ cup of pasta water, then drain and keep warm.

Heat one tablespoon of oil and butter in a pan over medium heat. Sauté chopped onions for 4 minutes, then add crushed garlic and sugar, cooking for another 2 minutes.

Add sliced mushrooms and cook for 4 minutes until golden. Pour in whisky and let reduce for 2 minutes.

Lower heat, stir in double cream, reserved salt, pepper, Dijon mustard, and balsamic vinegar. Heat through for 2-3 minutes.

Remove from heat, fold in grated parmesan and chopped parsley. Add drained pasta, tossing to coat, adjusting consistency with reserved pasta water if needed.

Slice the rested steak against the grain and add to the pasta mixture, gently tossing to combine.

Serve hot in bowls, garnished with additional parsley, grated parmesan, and black pepper.