1. Clean lettuces by swishing them through a large bowl or sink filled with cool water. After you swish the greens, they will rise to the surface; the sand and sediment will fall to the bottom of the bowl or sink. Once the sand and sediment are washed away, lift greens from water and transfer to a salad spinner; spin until dry.

2. Tear lettuces into bite-sized pieces. If you aren't going to use the greens immediately, wrap them in a clean kitchen towel, transfer to a plastic bag, and refrigerate.

3. Next, make the vinaigrette. Combine vinegar, mustard, salt, pepper, and sugar if using, in a small jar; shake to blend. Add oil, and shake again until emulsified.

4. For best results, use four parts greens to one part dressing and three parts oil to one part acid (vinegar, citrus juice, or a combination of both).