Garlic Mayonnaise (Aioli)
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Yields about 1 cup

4 large cloves garlic, mashed and peeled
1 teaspoon Dijon mustard
1/4 to 1/2 teaspoon salt
1 whole egg
1 egg yolk
1/4 cup fresh basil leaves (optional)
3/4 cup olive oil
Lemon juice to taste

Put the garlic cloves with the mustard, salt, pepper, egg, egg yolk, and 
basil in a blender. Blend a few seconds. While the blender is on, add ¼ cup 
of the oil, blend thoroughly, then add remaining oil slowly in a thin, 
steady stream until the mayonnaise thickens. Add lemon juice to taste.

From: http://www.sallybernstein.com/food/columns/fussell/garlic.htm