Heat the butter and a good glug of NOMU Extra Virgin Olive Oil in a frying pan, add the onions and NOMU Provençal Rub and sauté for a couple of minutes. Reduce the heat to low and cook the onions for about 20 minutes or until they are sweet and soft. Remove from heat and allow to cool.
Preheat oven to 200 °C. Roll the puff pastry out gently into a rectangle or square about ½ cm thick and score a border approximately 2 cm in from the edges. Spread the cooled onions evenly over the pastry and arrange the anchovies neatly in a lattice pattern over the onions. Scatter the sundried tomatoes and olives on top and season with NOMU Sea Salt and NOMU Black Pepper. Be cautious with the salt, as the anchovies are quite salty.
Place in the oven and bake for about 20-30 minutes or until the pastry is cooked through, puffed up and golden brown. Remove from the oven and garnish with fresh basil and dollops of pesto just before serving.