Heat butter in a pan, add chopped onion and cook just until lightly brown.
Add minced garlic, all seasonings and cook for one minute more.
Add tomatoes, cover with a lid and cook for 5 min on low.
Pour in chicken broth and bring to a boil. Return the lid back and continue to cook for 10 minutes or until tomatoes are tender.
Prepare the croutons (if using): transfer keto bread cubes to the baking tray, sprinkle with grana padano and bake for 10 minutes at 220 F/ 110 C.
Season the soup with salt and pepper and puree using an immersion blender.
Return the soup to the stovetop, add heavy cream and shredded cheese and warm it up.
Serve in a bowl garnished with grated grana padano and croutons (optional).