Preheat the oven to 180C/350F/gas mark 4. In a large frying pan, saute the shallots then the mushrooms in butter or oil until just tender. Season to taste.
Add the garlic and blue cheese. When the cheese just starts to melt, add the cream and reduce until thick. Add the tarragon.
Put the mixture into a heatproof bowl suitable for serving, or four individual bowls. Combine the two breadcrumb types and scatter over the mix.
Bake for 20-25 minutes until golden brown and then serve.