Used Wilton tip 125..with wider end of tip pointed toward cake and thinner end away from it. Turn cake as you pipe. Will post pics of tutorials soon. Used some scrapbook paper for top decor.
Just line jar with cupcake liner, batter should be about 1/3 full , place on baking sheet and bake per recipe directions. I made blueberry muffins this morning at 400F, jars did fine ..no breakage.