Cook chicken according to the directions of the Pan-Roasted Chicken Breasts recipe. Transfer chicken to platter to rest. Using potholder to protect hands from hot skittet handle, pour off most of fat from skillet; add garlic, then set skillet over medium-high heat and cook, stirring constantly, until light brown, about 1½ minutes. Add chicken broth, sherry and thyme; increase heat to high and simmer rapidly, scraping skillet bottom with wooden spoon to loosen browned bits, until slightly thickened and reduced to about¾ cups about 5 minutes. Pour accumulated chicken juices into skillet, reduce heat to medium, and whisk in butter 1 piece at a time; add½ teaspoons lemon juice and season to taste with salt and pepper.