2 tablespoons (1/4 stick) butter, room temperature
2 tablespoons dried herbes de Provence*
1 tablespoon coarse kosher salt
2 (3 1/2-pound) chickens
*This dried herb mixture can be found in the spice section of supermarkets and specialty foods stores. If unavailable, use a mix of dried thyme, basil, savory, and fennel seeds.