Preheat your oven to 400 degrees Fahrenheit. Slice the tops off the garlic bulbs and drizzle with olive oil. Wrap in foil and roast for 40-45 minutes until soft and golden.

Let the garlic cool, then squeeze the cloves into a bowl to make a paste.

In a large pot, heat butter and olive oil over medium heat. Add diced onions and sauté until translucent.

Add cubed potatoes and thyme, stirring to coat. Mix in the roasted garlic paste.

Pour in the stock and bring to a boil. Reduce heat, cover, and simmer for 20-25 minutes until potatoes are fork-tender.

Blend the soup until smooth. Return to heat, stir in cream if using, and season with salt, pepper, and lemon juice. Adjust seasoning as needed.

Serve hot.