Preheat oven to 200 degrees.
Lightly fry the mushrooms in garlic butter and freshly ground black pepper and set aside.
Boil the baby potatoes in a large pot of salted water over medium-high heat, until cooked. Remove from stove and drain the water. Allow to cool down for 5 minutes. Then halve some potatoes and leave others whole. Toss the potatoes, mushrooms and finely chopped fresh rosemary and a drizzle olive oil together, and season well.
Spread the potato mixture and cherry tomatoes out on a roasting tin and roast in the preheated oven until tender and golden brown, about 30 minutes.
Transfer the roasted goodies to a serving bowl, toss with the basil pesto and fold in the toasted pecan nuts. Sprinkle with salt flakes and garnish with basil leaves.
