1 Preheat the oven to 210 °C (th 7). Remove the thyme, mix it with 3 spoonfuls of mustard. Salt and pepper the filet mignon, brush it with thyme mustard. Then roll it in the poppy seeds.
2 Peel and finely chop the onion. Spread it in an oven dish and place the filet mignon on top. Pour the white wine and put in the oven for 25 minutes. Remove the meat from the dish, keep it warm, under a sheet of aluminum foil.
3 Strip and chop the chervil. Heat the oven dish over high heat, pour in the cream and the remaining mustard. Mix for 2 minutes, add the chervil and remove from the heat. Slice the filet mignon, coat it with sauce and serve with tagliatelle for example.