However, I was talking about the item, 'la bollería', not the woman eating it. The same question applies if it were a man eating it - should the one, the 'uno', agree in gender with the noun it replaces, which in this case is feminine, and should therefore be 'una'..?

whether it is a woman or una bolleria that does not dictate that any individual part of it should also be feminine

 as i understand it a bolleria is a selection of different breads not one thing. i may be wrong.

 a panederia is feminine but pan is masculine

I think bolleria is the breadbasket

No somos comprar las bollerias, solo compraríamos pan de diversos tipos

We aren´t buying baskets of bread, we are only buying bread of various types.

pan (bread) is masculine, bollo (sweetroll) is masculine,

paecillo and pancito (roll) are masculine, and bolillo (mexican usage for roll) is masculine.

There may be feminine pastries in the feminine noun - bread basket, but chances are there will be at least one masculine thing and that makes the masculine the proper gender.

"Bollería" is a tricky word here, because we don't have an English equivalent.  It's a singular word that encompasses the class of things that are personal-sized baked items made from dough meant to accompany your meal. 

In Spanish, it's a "mass noun," which means it's not usually countable; it's not easily pluralized.  In English, the word "Jell-o" behaves in the same way.  For example, if you say "Jello isn't free, they're going to charge you for each one."

If you WERE to count "bollerías" it would usually be an amount too large for Esti to eat at breakfast; e.g., las bollerías de Vietnam y de Senegal son pocas conocidas en China.  The Vietnamese and Senegalese roll-baking tradtions are not well-known in China.   It would be too much for Esti to eat her way through an entire roll-making tradition, let alone those of two countries!

So what is the antecedent of "cada uno each one"  in the sentence in the dialog?

If you're in that hotel restaurant, sitting at the table, and you're trying to warn Esti to stop eating the bollería, "cada uno" is each item, or each unit... each piece of bollería.  "Uno" when it means single unit or single item is masculine. 

¿Qué es el plural de pan dulce?

Si estoy en México y quiero ordenar dos panes, ¿qué pido?

Por ejemplo, “Señorita, tráigame dos panes dulces por favor?”

O, “Señorita, tráigame dos pan dulces por favor?”

¿Cuál es la forma correcta?

¡Gracias de antemano!

Algo tarde.

Pero si se dice: dos panes dulces. Es correcto.

SLDS