Question: Did they eat bread and butter in period?
The short answer is, "Most likely, yes."
Johnna Holloway provided a list of references to bread and butter that she extracted from the EEBO-TCP (a text database project currently under development). While these references are all from late period, they make it clear that eating bread and butter is a common practice at that time. Considering the consistency of culinary practice in the medieval period, it is most probable that bread and butter were eaten throughout.
Below is a selection of those references.
AN excellent & approued thing to make them slender, that are grosse.
Let them eate three or fowre cloues of Garlyke, with asmuch of bread and
butter euery morning and euening, first and last: neyther eating nor
drinking of three or fowre howers after their taking of it in y^e
morning, for the space of fouretene dayes at the least: and drinke
euery daye three good draftes of the decoction of Fennel, that is: of
the water wherein Fennell is sodde, and well streyned, fowretene daies
after at the least, at morning, noone and night. I knewe a man that was
maruelous grosse, and could not go a quarter of a myle, but was enforst
to rest him a doosen tymes at the least: that with this medicine tooke
away his grosnes, and after coulde iourney very well on foote.
(Page 49)
She abhorred then bread & butter, and other such natural foode. Wherby
she was maruelously consumed with a fluxe, and she yet lyueth, hauing
nothing on her but skyn and bone. I sawe her in Iune. 1577. She was
borne in Chayrsey, within two or three myles of Stanes, at which tyme
she was full three yeares of age.
(Page 130)
[Source: Lupton, Thomas. A thousand notable things, of sundry sortes Wherof some are wonderfull, some straunge, some pleasant, diuers necessary, a great sort profitable and many very precious. ... (1579) ]
When no butter could sticke on their bread, in in that part of the
citie, the greater number of the rebels assembled to Thomas his court,
and marched to saint Thomas his street, rasing downe the partitions of
the row of houses before them on both sides of the street, finding none
to withstand them: for the inhabitants fled into the citie, so that they
made a long lane on both the sides like a gallerie, couered all ouer
head, to shield as well their horssemen as their footmen from gunshot.
(Page 93)
[Source: The first and second volumes of Chronicles comprising 1 The description and historie of England, 2 The description and historie of Ireland, 3 The description and historie of Scotland: first collected and published by Raphaell Holinshed, William Harrison, and others... (1587) ]
No Butter cleaues nor sticks vpon my bread,
No Honny-combes will breede in my bare hyue:
My gold but glasse, my siluer worse then lead,
My luck as bad as any man alyue;
(Page 11)
[Source: Churchyard, Thomas, 1520?-1604. A feast full of sad cheere vvhere griefes are all on heape: where sollace is full deere, and sorrowes are good cheape. (1592) ]
And if any man desire a light nourishing, and comfortable breakfast, I
know none better then a couple of potched eggs, seasoned with a litle
salt, and a few cornes of pepper also, with a drop or two of vinegar, if
the stomacke be weake, and supped
off warme, eating therewithall a litle bread and butter, and drinking
after a good draught of pure. Claret wine. This is an excellent
breakfast, and very comfortable for them that haue weake stomacks. Eggs
moderately vsed are accommodate for euery age, and constitution,
especially for the elder sort of people, and such as want bloud; but
soonest offensiue to the cholerick and sanguine, for whom in hot seasons
they are not conuenient.
(Page 87-88)
[Source: Venner, Tobias, 1577-1660. Via recta ad vitam longam, or A plaine philosophical discourse of the nature, faculties, and effects (1620) ]
and the low-Countrie men many times doe, who commonly vse to feed of Cresses with bread and butter. It is eaten with other sallade hearbes, as Tarragon and Rocket: and for this cause it is chiefely sowen.
[Source: The herball or Generall historie of plantes. Gathered by Iohn Gerarde of London Master in Chirurgerie very much enlarged and amended by Thomas Iohnson citizen and apothecarye of London. (1633 edition) ]