Let the pastries thaw next to each other, then roll out so that they overlap and brush with a little butter. Peel garlic and chop finely. Peel onions and chop.
Sauté garlic and onions in a skillet in hot oil until translucent and set aside.
Preheat the oven to 160°C (approximately 320°F) convection.
Rinse broccoli, carrots, celery and bell peppers, pat dry and cut into small pieces or cubes, making sure to remove the ribs and seeds of the bell pepper. Blanch for about 1 minute, rinse in cold water and drain. Pour the sour cream, eggs, cheese and basil in a bowl and mix well, season with salt, pepper and nutmeg and mix with the blanched vegetables and cooked onions. Spread onto the pastry, carefully roll up the strudel and bake in the oven for about 45 minutes until golden brown. From time to time, repeatedly brush with the remaining melted butter. Remove from oven, slice and serve with herbed creme fraiche, if desired.