In a large pot or Dutch oven, melt butter over medium heat. Add onion and cook, stirring, until softened. Add chicken broth and thyme.

If using raw frozen vegetables, add them now. Bring to a boil, then reduce heat and simmer until vegetables are tender, 15-20 minutes.

If using cooked frozen vegetables, bring stock to a boil, then add frozen vegetables. Reduce heat to medium-low and allow to cook a few minutes, until vegetables are warmed.

Using an immersion blender or in batches in a blender, puree soup until smooth. Return to pot and over medium heat, add the Half and Half/cornstarch mixture. Cook stirring, until mixture is warmed and slightly thickened. Taste and season with salt and pepper to taste.

For croutons: Pre-heat oven to 400° F. Add diced bread to a large bowl. Drizzle with oil and sprinkle with salt, pepper and thyme. Toss well. Spread evenly on a baking sheet and cook in pre-heated oven for 8-10 minutes, stirring a few times, until golden. Allow to cool on baking sheet.