The tartine is a french open-faced sandwich that is usually served with an elaborate or fancy spread. Despite its 'frenchness', with a little patience and imagination, the tartine is actually quite simple 'dish' to make. Preparation of this open face sandwich calls for deft patient hands and a good knowledge of complementing flavors using just a few ingredients. Understanding how certain foods (and cheeses) may be cooked at high temperature also helps. Herbs which are packed with flavors but occupy little space are great ingredients to use. (I have a idiosyncratic peeve of open-faced sandwiches with ingredients falling off all over the plate).
A delish and quick-to-fix tartine combination is the mushroom tartine. Although raclette is often the preferred cheese, you may consider experimenting with a variety of cheeses such as Gruyere, Emmenthaler, Brie or even Gorgonzola! Many bistrots in France serve tartine that are topped with ingredients that were already cooked before the sandwich is put into the broiler, for example roasted tomatoes, peppers or chanterelle. However with mushrooms you may skipped that step and yet not compromise for a rich and flavorful tartine because mushrooms cooked very easily over high temperature. To do this, layer the cheese over your preferred slice of bread ( I like a rustic artisanal loaf that is also suitable for bruschetta), then a few basil leaves (or whichever green you fancy), and then after which you may put on the sliced mushrooms. When all's done, they are ready to be broiled!. I would suggest that the rack to be placed further away from the broiler as you would for cooking meat. Keep the temperature at a moderate 160-170 degrees celcius and broil the tartine for about 15 minutes. The trick is to choose the cheese that would melt slowly during the cooking time of the mushrooms. With mushrooms in season now, and the dining festivities around the corner, this cannot be a greater time to have the tartine for lunch, saving your calorie upload for dinners with friends and loved ones!