Although it makes a delightful breakfast, the frittata could also be served with a green salad for a lunch or light dinner. White button mushrooms can be substituted for the shiitakes; trim but do not remove the stems.
Cook the vegetables, then add the seasoned eggs, and bake the frittata -- all in one pan.
Vinaigrette is a simple blend of oil, vinegar, salt, and pepper. Mustard is also commonly added. You can also add an extra flavoring or two, such as herbs, scallions, garlic, cheese, horseradish, poppy or sesame seeds, or a bit of sugar or honey. If you're using fresh herbs, add them just before using the dressing.
Freezing the tenderloin or sirloin for about 20 minutes will make it easier to slice. For thin, even slices, place each beef slice between two sheets of plastic wrap and pound them with a meat mallet or small skillet.