Whisk den miso ingredients in a pan over medium heat until dissolved and set aside to cool.
Combine tamarind, den miso, garlic, and thyme in a bowl and marinate steaks for at least 3 hours.
Heat oil in a heavy saucepan and cook spices, ginger, chilli, and coriander until aromatic.
Whisk sifted besan and water together in a bowl until the mixture is smooth.
Stir the paste into the spiced oil for 10-12 minutes over moderate heat until thickened.
Pour mixture onto a tray sprinkled with nigella seeds and polenta, then chill until hardened.
Heat a griddle or frying pan over high heat until hot.
Brush steaks with oil, season, and cook for 2-4 minutes on each side.
Rest the steaks on a rack covered with foil for 10 minutes.
Preheat a deep-fat fryer with vegetable oil to 180°C.
Cut the chilled besan into chips and dust them with polenta.
Deep-fry the chips for 2-3 minutes until golden-brown and drain on kitchen paper.
Whisk molasses, vinegar, and olive oil together to dress the watercress.
Serve the steak with chips and the watercress salad alongside.