Blanch the basil: This preserves the bright green color. Start a small pot of water to boil. Prepare a bowl of ice water. Remove the basil leaves from the stem and wash them; measure out 1 packed cup of leaves (make sure to pack the cup full for the best flavor). Once the water is boiling, add the basil and boil until bright green, 30 seconds to 1 minute.
Immediately turn off the heat, remove the basil and plunge it into the ice bath. Once the leaves are cool, remove them from the water and squeeze out as much excess water as possible.
Blend the sauce: Place the blanched basil, olive oil, garlic and salt in a blender or in the cup for an immersion blender. Blend until fully combined. Taste and add lemon juice and additional salt to taste. Use immediately or refrigerate for up to 1 week.