“נשיכה.” If there are two identical doughs – both without the minimum shiur or one with the shiur and one without – and one does not care if they get mixed together, they can be connected through נשיכה. This is when the two doughs touch to the point that they stick together a bit, such that if they were to be separated, each dough would remove some of the other dough. If this is done, one can do hafrasha from one of them (שו''ע סי' שכ''ה ס''א, ובט''ז שם סק''א ). However, merely touching them together does not combine them for the shiur to require hafrashas challah.
Most poskim hold נשיכה only works on dough, in which case hafrashas challah is done with a bracha. If the נשיכה happened during the baking process, some hold it still works. Therefore, the hafrasha should be done without a bracha (חלה כהלכתה סי' ח' אות ה'). If נשיכה was done post-baking, most poskim hold hafrasha is not done.
One basket. Two doughs can also be combined if they are placed into the same basket, or any other vessel with an interior (שו"ע שכ"ה ס"א ), provided they do not completely protrude out of the vessel (רמ"א ). L’chatchila, they should be touching (ש"ך בנקה"כ ). However, if they were placed on one tray, shelf, table, etc., they do not join.
This method works while they are dough, or after they are baked (פתח"ז כלל ו' ס"א ) – even long after they are baked (או"ז ח"א סי' רכ"ו, מנ"ח מצוה שפ"ה ) – and the bracha is made (שו"ת רב פעלים ח"ד סי' ל"ו ).
With a cloth. Covering the loaves with a cloth is like putting them in one vessel. The same cloth should be beneath the loaves and also covering them on top (ש"ך סק"ה, פמ"ג סי' תנ"ז מ"ז סק"א ). Some hold they need not be covered by the same cloth, and they can even be covered with a dish (ביאה"ל סי' תנ"ז ס"א ד"ה והסל ).
