In a 10- to 12-inch ovenproof frying pan over high heat, boil wine and shallots, stirring often, until liquid evaporates, about 12 minutes.
Add broth to pan; boil until reduced to 1 3/4 cups, about 12 minutes. Stir in tomato paste and half the sage; simmer over medium heat for 2 minutes. Pour sauce into a bowl and add 1 tablespoon olive oil. Rinse and wipe pan dry.
In another bowl, combine remaining sage, mustard, thyme, and garlic.
From a long side on each breast, pull chicken skin almost free, leaving attached on the opposite edge. Smear exposed areas evenly with mustard mixture. Neatly lay skin back in place.
Place frying pan over high heat and add 2 teaspoons olive oil. When hot, add chicken, skin down, and brown well, 2 to 3 minutes. Do not turn pieces.
Place pan in a 450° oven and bake until chicken is no longer pink in thickest part (cut to test), about 15 minutes. Discard fat from pan. Set each chicken piece, skin up, on a dinner plate; keep warm.
Add sauce to pan and stir over high heat until simmering. Spoon sauce equally around chicken. Season to taste with salt and pepper.