In a large serving bowl, combine the lemon juice, olive oil, garlic, mustard, maple syrup or honey, shallot (optional), salt, and pepper. Whisk to emulsify.
SALAD: To the same bowl, add the snap peas, basil, and pistachios and toss to combine and coat with the dressing. Taste and adjust as needed, adding more lemon juice for brightness, maple syrup for sweetness, or salt to taste.
Garnish with additional basil and pistachios and the red pepper flakes (optional). Serve right away.
Best when fresh. The dressing can be made up to 3 days in advance by adding the ingredients to a jar with a lid and shaking to combine. Let it come to room temperature before tossing with the snap peas, basil, and pistachios. Not freezer friendly.
*Loosely adapted from NY Times Cooking. *Nutrition information is a rough estimate calculated without optional ingredients.