Vegetarian stroganoff pasta bake with mushroom and spinach

Ingredients

• 500g dry penne pasta
• 50g butter
• 1 onion, halved, thinly sliced
• 2 garlic cloves, finely chopped
• 3 sprigs thyme
• 400g each Swiss brown and button mushrooms, cleaned and sliced
• 1 tbsp olive oil
• 3 cups baby spinach leaves
• 50g tomato paste
• 2 tsp sweet paprika
• ¼ cup plain flour
• 3 cups vegetable stock
• 250g sour cream
• ¾ cup grated cheese
• 2 tbsp finely shredded parsley, to serve
• freshly ground black pepper, to serve
• additional salad leaves, lightly dressed, to serve