Finely dice one shallot into small, even pieces and set aside.

In a glass mason jar or small mixing bowl, combine the diced shallot, olive oil, red wine vinegar, lemon juice, and Dijon mustard. Sprinkle in red pepper flakes if desired.

Blend the ingredients together using a whisk or fork until smooth. If using a mason jar, shake well with the lid secured.

Let the dressing rest for at least 5 minutes at room temperature to meld the flavors.

Taste the dressing and adjust seasoning with salt and pepper as needed.

Store any leftover dressing in an airtight container in the refrigerator for up to 2-3 weeks.