Roast the Garlic: Preheat your oven to 375°F. Slice the top off a whole garlic head to expose the cloves. Drizzle with olive oil and lightly season with salt and pepper. Wrap in foil, place on a baking sheet, and roast for 40–45 minutes until soft. Let it cool, then squeeze the garlic cloves out.

Boil the Potatoes: While the garlic roasts, boil the peeled potatoes in a large pot of water until fork-tender, about 15 minutes. Drain, let cool slightly, and dice into chunks.

Sauté the Aromatics: In a large pot or Dutch oven, melt the butter over medium-high heat. Add the chopped onions and sliced leeks. Cook for 6–8 minutes until softened and translucent.

Build the Soup Base: Lower the heat to medium. Stir in the flour and cook for 1–2 minutes until slightly golden. Slowly pour in 4 cups of broth, milk, cream, thyme, and a pinch of salt and pepper. Bring to a gentle boil, then simmer for 2–3 minutes until slightly thickened.

Blend the Soup: Add the boiled potatoes, roasted garlic, and parmesan. Use an immersion blender to puree until smooth. Add up to 1 more cup of broth if needed to adjust the thickness.

Season and Serve: Taste and adjust with more salt and pepper if desired. Serve hot, topped with extra parmesan, chives, or crushed crackers.