Step 1 Put the eggs in a blender and blend just until completely smooth.
Step 2 Heat a high-quality 10-inch nonstick pan over low heat. Add the oil and butter. When the oil and butter have warmed, add the eggs. Allow them to cook slowly without moving the pan. When the eggs have set and are nearly cooked through, after several minutes, use a spatula to ensure that the omelet is loose.
Step 3Add the creme fraiche and, using the spatula, fold one-third of the omelet over onto itself and then slide the folded edge onto the plate. As the omelet settles onto the plate use the angle of the pan to fold the final third over, making a perfectly rolled omelet. Remember that the omelet will continue to cook a bit once it is rolled and on the plate, so take this into consideration in judging when to remove the eggs from the pan.
Step 4Sprinkle with salt to taste and, if desired, garnish the omelet with a sprinkling of freshly chopped herbs.