Preheat the oven to 200°C.
Boil potatoes in salted water for 12 to 15 minutes.
Drain, dry, and rice the potatoes before mixing with 150g butter and cream.
Season steaks with salt and heat a large ovenproof pan over high heat.
Fry steaks and halved shallots in 25g butter and oil for 2 minutes per side.
Oven cook the pan for 6 to 8 minutes for medium steaks.
Remove meat and shallots to a plate to rest.
Fry chopped shallots and garlic in 25g butter for 3 minutes.
Melt caster sugar until golden, add wine, and reduce by half.
Add stock, simmer for 3 minutes, then heat through the snails.
Whisk in the final 25g butter and stir in fresh herbs.
Serve steak topped with a halved shallot, snail sauce, and mash.