This creamy sauce makes a great accompaniment to Potato Croquettes, as well as cold chicken, fish, or shellfish.
Roast pepper directly over the flame of a gas-stove burner or under a broiler, turning often, until lightly charred on all sides. Place in a bowl, cover with plastic wrap, and steam 10 minutes. Scrape blackened skin from pepper, then cut in half, remove seeds, and coarsely chop.
Put bell pepper, egg and yolk, garlic, mustard, vinegar, and salt in a food processor. With machine running, add 1/2 cup olive oil, 1 teaspoon at a time. Pour in remaining 1/4 cup olive oil and the canola oil in a slow, steady stream, processing until emulsified. Transfer to a bowl, and stir in olives, parsley, capers, creme fraiche, and lemon juice.