How to Make It
In a small bowl, soak the porcini in hot water until softened, about 30 minutes. Scoop out the mushrooms.
In a medium skillet, melt the 1 tablespoon of butter until foamy. Add the porcini and cook over moderately high heat, stirring occasionally, until lightly browned, about 5 minutes. Add the garlic and thyme and cook for 1 minute. Transfer to a plate and let cool.
In a food processor, pulse the olives and porcini until finely chopped. With the machine on, add the olive oil and truffle oil and process to a paste. Transfer the tapenade to a bowl and season with salt and pepper.
Preheat the oven to 350°. Lightly brush a baking sheet with a little of the melted butter. Brush the bread slices on 1 side with the remaining butter. Using a 1 1/4-inch round biscuit cutter, stamp out 4 rounds from each slice of bread. Arrange the rounds, buttered side up, on the baking sheet and sprinkle with the Fontina. Bake for 6 to 8 minutes, or until the rounds are golden on the bottom and the cheese is bubbling.
Arrange the canapés on a platter and top each with 1 teaspoon of the tapenade. Garnish with the chives and serve.