One of the neat tricks I've learned from talking with caterers and the like is that when you're cooking rice for a lot of people (e.g. 120) you can bake rice instead of boiling it. The rice goes into a steamer pan with the same amount of water that you'd use to boil it, and then it's covered tightly and put into an oven for an hour. This method has the benefit of being less time-sensitive than boiling, and you don't have to worry about it burning on the bottom as the stuff in 30 quart stockpots often do.
A couple of days back I decided to try cooking frumenty this way. Frumenty is essentially a thick cracked-wheat porridge. I've tried making it at a feast once or twice and it always gave me trouble. Sometimes it just took too long to cook, other times it burned. The wheat is boiled in the same way as rice, so it seemed like a perfect candidate for baking.
I put a cup of cracked-wheat into a deep glass baking pan along with two cups of water, covered it with aluminum foil, and popped it into a 350°F oven. An hour later I took it out to check on it - huh ... too soupy and the grains were still a bit too crunchy. Back into the oven it went. I checked it another hour later and it was perfect. So frumenty can be cooked this way, and it is a lot easier, but it takes longer. Not a bad trade-off. I'll have to remember to update my recipe for frumenty to reflect this.
Days later the thought occurs to me: did they ever bake grain in the middle-ages instead of boiling it? This can be a hard sort of question to answer for certain, but I can look for evidence in the medieval cookbooks. There are lots of medieval recipes for rice, and at least a couple from each country. I start reading through them and after a while things begin to blur - they all sound about the same. Wash the rice, put in a pot with some liquid (e.g. water, broth, milk), and boil. Some add other things like meat or rice-flour or almond milk. Some add saffron or other spices. All of them say to boil it.
I didn't find a single recipe for rice or wheat that said to put it in a pot with liquid, cover it, and bake it. Ugh.
So then I'm forced to ask myself why? This is a cooking method that is perfectly suited to medieval European cuisine. The dish will turn out perfectly for a huge range of time and temperature. Why wouldn't they cook it this way? I don't have an answer for this, but I will veer off into speculation for a moment here.
The setup of the medieval kitchen, and especially the oven, was functionally different in a couple of significant ways. The ovens were usually heated up early in the morning by filling them with wood and sealing them up. When the oven was hot enough (around 500°F) the ashes were shovelled out, the floor of the oven was wiped out, and the bread baking began.
Interestingly enough, the ovens were often in a separate room from the kitchen. Sometimes they were in a completely different building. In small towns you could take your bread dough to the baker to bake it in their oven. While boiling rice is easy enough over a fire, and baking it is easy in a modern kitchen, it would be much more awkward to do if the oven were elsewhere. Not impossible, mind you, just more awkward.
I suspect that it just never occurred to any medieval cook that they could bake rice. Heck, it didn't occur to me, and I've got an oven right in my kitchen that heats to a consistent temperature at the push of a button. We modern cooks also use our ovens for a larger variety of foods - we "roast" meats there instead of over an open fire, and we bake vegetables like potatoes or turnips. In the middle ages, ovens were generally used for bread and pies - things made of or enclosed in dough.
So it looks to me like baking rice is one of those thinks like the sandwich. They could have done it - they had all the stuff to do it - but they just never had the idea, and so they didn't.
Of course I could be wrong, and I'd be overjoyed if someone found a recipe for baking grain instead of boiling it.