Add shallots and garlic to pan and cook over medium heat, stirring, until translucent, about 5 minutes. Add chili powder and mustard and cook, stirring, 1 minute. Increase heat to high; add bourbon and maple syrup. Bring to a boil, scraping up browned bits. Add vinegar and brown sugar and return to a boil. Add reserved bacon; reduce heat to low. Simmer, stirring occasionally, until liquid reduces to a thick glaze, about 10 minutes.