Preheat the oven to 180°C and lightly spray a 12-hole medium muffin tray.
Place one sheet of filo flat on the bench and brush with butter. Top with another sheet of filo and smooth down. Set aside and repeat this step with remaining filo. Cut each set of filo widthways into four strips so you have 12 strips in total.
Take a strip and lay it over one of the muffin holes, then fold it back and forth, changing the angle slightly, to cover the hole. Press into the base of the hole to make a nest. Repeat with remaining filo strips and chill until needed.
Whisk together the eggs, cream, parmesan and celery salt, and set aside. Heat the olive oil and sauté the bacon, onion and pine nuts until the bacon is crisp, the onion tender and the pine nuts toasted. Add spinach and allow to wilt.
Divide the bacon mixture evenly between the filo nests, top with diced brie and pour over the egg mixture.
Bake for 15-20 minutes until golden and puffed.