Pre-heat the oven to 200°C.
Butterfly the pork fillet down its middle, opening it up flat. Sprinkle the fennel seeds and some seasoning down the centre line of the fillet. Fold the fillet back up around the fennel seeds into its original shape. Tie well using kitchen string/twine.
Rub the fillet with the groundnut oil and season well on the outside. Heat a large heatproof frying pan over a moderate heat until hot. Seal the fillet until golden brown in colour all over. Transfer to the oven and roast for 20-25 minutes until the pork reaches 70 degrees on a meat thermometer.
Meanwhile, cook the fennel in a large saucepan of salted, boiling water until tender; usually 10-15 minutes. Drain and transfer to a food processor. Add the crème fraiche and some seasoning and pulse until you have a thick puree. Spoon into a saucepan and reserve to one side ready to reheat later on.
Remove the pork fillet from the oven when ready and cover with aluminium foil, leaving it to rest for 5-10 minutes to one side. Place the cherry tomatoes on the vine on a roasting tray and drizzle with the olive oil. Roast for 5 minutes as the pork is resting. Remove the cherry tomatoes after 5 minutes and reheat the fennel puree at the same time.
Start cutting the pork fillet into medallions and serve on nonstick baking paper with the roast tomatoes and the fennel puree to one side.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home.