One day in this week בני אשכנז may follow the פסק of the מחבר in שלחן ערוך. ? There is a מחלוקת between the מחבר (Bais Yosef) and the רמ"א. The B.Y. allows tasting food on a תענית if it is not swallowed. The רמ"א forbids tasting food on a תענית even if not swallowed. The משנה ברורה writes if one cooks for a סעודת מצוה then we may rely on the B.Y. and one may taste the food on a תענית. When עשרה בטבת falls on a Friday (this year) then we have a מצוה of (טועמיה (מג"א plus the food is being cooked for סעודת שבת. We may assume that the מ"ב would surely agree, one may be lenient like the מחבר and taste the food without swallowing .אמבצי