Add the kale, Romaine, croutons, Parmesan, dressing, and tomatoes (if using) to a large bowl. Toss until combined.
Serve immediately.
Add all ingredients except milk to a small mixing bowl, and whisk together until combined and smooth. Whisk in a tablespoon of milk at a time until the dressing reaches your desired consistency.
Use immediately, or refrigerate in a sealed container for up to 3 days.
