Heat the olive oil in a large skillet over medium heat. Fry the shallot until translucent and fragrant, about 3 to 5 minutes. Add the garlic and mushrooms and continue to fry until the mushrooms start to soften, about 5 minutes. Stir in the tomato paste, sugar, salt and pepper and leave to cook for a couple more minutes. Add the diced tomatoes and fresh thyme. Cover and simmer on low for 30 minutes.
Remove the lid and stir in the worcestershire sauce. Taste and adjust the salt and pepper as you like. There should not be very much liquid left in the pan. If there is, simmer uncovered until the liquid has evaporated. Serve over some toasted slices of bread. Garnish with fresh chervil if desired.
I have used cremini mushrooms here, but this recipe would also work well with morels, porcini or oyster mushrooms. I find the quickest way to chop the mushrooms is to pulse them a few times in a food processor.