Preheat oven to 350 degrees. Spread tomatoes on a large baking sheet with 1/4 c olive oil, onions, garlic, and 1/2 t salt and pepper. Roast for 25 minutes.
Add tomato mixture to large dutch oven along with artichoke hearts, and chicken stock. Bring to a boil over medium heat reduce and simmer for 40 minutes. Blend with an immersion blender or in the cuisinart, leaving some chunks. Add salt and pepper to taste, finish with 1/4 c greek yogurt, stir, Serve with warm baguette slice and chopped fresh basil. Add more chicken broth if it is too thick