Combine the soy sauce, oil and Worcestershire sauce in a bowl and add the garlic and pepper. Pour the marinade into a freezer bag, place the tenderloin in the bag and seal. Move the tenderloin around until completely coated in the marinade, then refrigerate for at least one hour – preferably longer.
Using a hand mixer, beat the crème fraîche with the egg yolk and the rest of the ingredients for 1 min. Season to taste, cover and refrigerate until serving.
Finely dice the cucumber and place in a bowl. Sprinkle with salt and leave for about 10 min. Cut the cherries into quarters. Combine the cherries, onions and chilli with the salted cucumber. Add vinegar, syrup and pepper. Season to taste and refrigerate.
Wash the potatoes, place in a pot and cover with water. Add salt and bring to a boil. Remove the pot from the heat and leave covered for approx. 10 min. Drain the potatoes and arrange them on 4 squares of baking parchment (approx. 38 x 42 cm in size). Top each pile of potatoes with lemon zest, butter, smoked salt, rosemary and pepper. Fold the parchment around each pile of potatoes and roll tightly along the edges to form a pouch. Heat up the barbecue nice and hot and grill the potato pouches using indirect heat for approx. 15 min. with the barbecue lid on.
Meanwhile, grill the tenderloin for about 20 min. – turning occasionally. Remove the tenderloin from the barbecue, wrap it in aluminium foil and keep warm.
Slice the tenderloin and serve with cherry salsa, the unopened potato pouches and the chilled Béarnaise. Garnish with whole cherries.
Wrap the potatoes in aluminium foil instead of baking parchment if you can’t cook the pouches on the grill using indirect heat.