I seen a few posting for doing something like automating a mill by various means. That might be fine for something to let the covenant staffing to work with long term. But I was wondering about how to do it with a one shot spell. Something like Mu/He Base 3 Change a plant, + 1 Change plant to treated or finished plant. +1 Touch/Momentary/Circle. Idea being you have a mount of wheat.. the magi just draws a circle around it and bam, it goes from seeds to ground flour. Am I missing anything?
Sounds exactly like Rego craft magic, using ReHe, to me. Take a look in Covenants or HoH: Societies (Jerbiton section) if you're not familiar with Rego craft magic.
You want Rego, not muto, for this. With muto the flour turns back into grain once the spell ends.
Rego Craft magic will require a finesse roll, especially to get fine flour (fine enough to cause explosions is noted as requiring a Finesse roll "too high to make a practical weapon" on page 135 of Tales of Mythic Europe, but you probably don't need it that fine for just making bread).
I was thinking similar to all the responses, thanks guys for verifying. Only reason I let muto confuse me was when i read the panels for muto vs rego
Muto
To change plants into
treated or finished material (for example,
wooden furniture, a vegetarian meal, linen
or cotton cloth) add one magnitude to the
level necessary to change plants into natur-
al, unworked plants.
Where as Rego ONLY talked about moving plants around.
Also, I know muto reverts. But I thought Muto had a couple useful exceptions. i.e. I turn a stone slab into mud mu/te. While it is mud I, I have my local artist mold the slab into a striking image of my ego 
. Once the spell ends it reverts back to stone. But it is still shaped into a statue. I thought muto would be doing to the wheat would be similar... It is still wheat, just reshaped into power. A little grey area in my thinking, but the rules can have some fuzziness in form/tech overlap.
I suppose that you could use Muto Herbam to turn the grain into some sort of paste and then roll or squish it out into a fantastically thin layer than let the Muto spell expire.
Consider these:
from : spellswiki.wikidot.com/magic-items
Flour Maker
A small grindstone is used to grind wheat by the covenfolk. Although it is small, it suffices for all of the covenant's needs easily, allowing it to store grain which it buys at the annual Festival from the nearby villagers to enjoy fresh bread all year around. The item is operated by a single covenfolk, traditionally the most agile (and, often, young) member of the kitchen's scullions. (The item provides 5 pounds in cost savings on food expenses.)
This item was made as a lesser enchanted device. The lab text describing it is in the covenant's library.
ReHe 35 (ReHe B5, +1 Touch, +1 Concentration, +2 Group, +10 levels unlimited frequency). This small grinding stone does the work of a whole mill, although it is only used intermittently by the covenfolk. A Dex + Finesse roll of 6 is required to operate it properly; a dexterous covenfolk is assigned to it, who would usually develop a low Finesse score by Exposure.
Contributor: Yair
TME 120-121 has Work of a Hundred Querns, which is the spell for doing this. It also mentions that an Int+Finesse roll of 6 will get you crappy flour - you need Int+Finesse of 12 to get the really good stuff.