Saute 1 chopped shallot with 1 tablespoon butter until the shallots are soft. Add the sliced mushrooms and saute until the mushrooms have released their liquid and it has evaporated. Set aside and keep warm.
In a separate pan, saute the remaining chopped shallot in 1 tablespoon butter. Add the snails and the garlic to the pan and toss. Remove the pan from the heat and add the Cognac. Ignite the Cognac with a lighter or by tilting the pan carefully towards the open flame and letting it catch. Flambe the Cognac until it is almost reduced. Add the Cabernet, bay leaf, and thyme, and reduce the liquid in the pan by two-thirds. Pour the veal stock into the pan and let the sauce simmer for 5 minutes.
After the snail mixture has simmered for 5 minutes, add in the mushrooms and remove from the heat. Whisk in the remaining butter and stir in the truffle oil. Adjust seasoning with salt and pepper and top with chives. Serve the snails divided between warm shallow bowls.