Peel and finely chop the onion.
Soften the gelatine in a bowl with some cold water.
In a saucepan, put the milk, cream, chopped onion, Parmesan and vinegar.
Bring to the boil then turn off the heat.
Off the heat, leave to infuse uncovered for 10 minutes.
Squeeze out the gelatine then add to the warm saucepan.
Blend with a hand blender then filter the mixture through a fine sieve.
Pour into 6 small glasses and leave to cool.
Refrigerate for at least 3 hours.
Prepare the sauce: chop the shallots and fry them in a saucepan.
Add the tomatoes and simmer uncovered over a low heat for 20 minutes.
Blend with a hand blender, season with salt and pepper and add the sliced sun-dried tomatoes.
Put to one side.
Heat a frying pan.
When it is very hot, add the morels (with no butter or oil) and cook for 10 minutes until all the water has evaporated.
Add butter to the pan, season with salt and pepper.
Pour the warm tomato sauce over the panna cotta and then arrange the morels on top.