In a small mixing bowl, place eggs, cream, mustards, salt and pepper. Whisk until combined; set aside. Wash and dry vegetables. Using a vegetable peeler or mandolin, slice long ribbons until most of carrot is ribboned; if using a peeler, keep peeling from the same side without rotating. Repeat with zucchini and yellow squash. Cut all ribbons in half, crosswise. Cut bell pepper into juliennes, approx. 1/2” wide, then trim length to fit the depth of the muffin cups.
Melt butter. Place one sheet of filo on work surface, short side close to you.
Start on one of the longer sides and brush the bottom half of the sheet with butter.
Fold unbuttered side over the buttered side.
Leaving the folded sheet where it is, brush just one half (right or left).
Fold the unbuttered side over.
Brush top with butter.
Repeat folding with a second sheet of filo.
Brush the top.
Place one on top of the other, crisscrossing them.
Place buttered layers into one of the muffin cups.
Make sure the filo is pushed tightly against the bottom and sides.
Tuck the ends of dough under, similar to piecrust. Repeat with the rest of the filo, to create six quiches.
Into filo-lined cups, pour some of the egg batter, about 1/3 way up.
Arrange vegetable ribbons on their side lengthwise, moving outwards in, alternating colors.
Do not place vegetables too close together, to allow batter to fill the spaces. Depending on the size of your vegetables, you may not need all of the ribbons. If using peppers, plug a few of them in the center, standing up for more color.
Gently pour more batter over each quiche, taking care not to fill more than 3/4 up the quiche. Lightly tap pan against the work surface to release air bubbles.
Bake in a preheated oven at 350° for 20 min, then rotate and bake 10-15 min more, until the crust is deep golden-brown and the batter has set. Remove from oven and let rest 10 min, then gently transfer quiches to a serving plate.
* Most filo packages contain 2 rolls of 20 sheets per roll. Use 1 roll for the recipe.