Place the flour in a bowl, making a well in the centre. Add the egg and half the milk and whisk to a smooth batter. Mix in the remaining milk and half the thyme. Leave to rest for 20 minutes.
Lightly grease a 20cm frying pan with a little of the oil, then pour in enough batter to cover the base. Cook for 45 seconds, flip over and cook for another 45 seconds on the other side until cooked through. Repeat using all the mixture. Set aside and keep warm.
Meanwhile, heat ½ tbsp oil in a large frying pan. Add the mushrooms and shallots and fry for 10 minutes, then remove from the pan and set aside.
Add the remaining oil to the pan. Add the butternut squash and sweet potato and fry for 5 minutes until golden. Add the stock, garlic and the remaining thyme, then cover and cook for 7-8 minutes, until the vegetables are just tender. Stir through the mushrooms and crème fraîche, then season and heat through.
To serve, place a pancake on each plate and spoon a generous amount of filling on to each. Roll up, cut in half on the diagonal and drizzle over a little of the sauce.