Toast garlic cloves in small skillet over medium heat, shaking pan occasionally, until fragrant and color of cloves deepens slightly, about 8 minutes. When cool enough to handle, skin and mince cloves (you should have about 3 tablespoons). Using dinner fork, mash garlic, the 2 cheese, Dijon, butter and salt in small bowl until thoroughly combined.
Adjust oven rack to middle position and heat oven to 500 degrees.
Spread cut sides of loaf evenly with garlic butter mixture; season to taste with pepper. Transfer loaf halves, buttered side up, onto baking sheet; bake, reversing position of baking sheet in oven from front to back halfway through baking time, until surface of bread is golden brown and toasted, 8 to 10 minutes. Cut each half into 2-inch slices; serve immediately.