Sweet Potato Zucchini Vichyssoise

Ingredients

• 1 Tbsp butter (or an additional Tbsp olive oil for a vegan version)
• 1 Tbsp extra virgin olive oil
• 5 cups chopped leeks, white and light green parts (I used 3 large leeks)
• 4 cups chopped peeled sweet potatoes (about 2 large potatoes)
• 2 cups chopped zucchini (1 large zucchini)
• 6 cups low-sodium vegetable broth
• kosher salt and freshly ground black pepper, to taste