Parsnip and horseradish soufflé with Gruyère AOP | Cheeses from Switzerland

Ingredients

• 125 g grated Gruyère AOP
• 600 g parsnips
• 300 g carrots
• 300 g leeks
• 2 large red onions
• 2 tbsp butter
• 2 eggs
• 100 ml milk
• 1 cup sour cream (180 ml)
• 1-2 tbsp finely grated horseradish
• 1 tbsp finely grated lemon zest
• 1 tsp thyme
• Salt and pepper