Easy Parsnip and Leek Soup (Creamy One-Pot Recipe)

Ingredients

• 2 tablespoons unsalted butter
• 1 tablespoon olive oil
• 3 medium leeks, white and light green parts only, sliced and rinsed
• 1 celery stalk, chopped
• 1 1/2 lb (680 g) parsnips, peeled and chopped
• 3 garlic cloves, minced
• 1 teaspoon fresh thyme leaves, or 1/2 teaspoon dried thyme
• 1 teaspoon kosher salt, plus more to taste
• 1/2 teaspoon black pepper
• 4 cups (950 ml) low-sodium vegetable broth, plus more as needed
• 1/2 cup (120 ml) heavy cream
• 1 tablespoon fresh lemon juice
• 2 tablespoons chopped fresh chives
• 2 tablespoons toasted pumpkin seeds
• Extra cream or plain yogurt, for swirling, optional