Has anyone ever made preserves a Dutch oven in the oven?

So glad it worked well for you! What did you roast them in, pan-wise? Peaches may be just different enough from the plums to take a bit longer. Glad you upped the temp so you were not stirring all day! And, SeaJambon, since we are talking spicing up the fruit, have you ever tried a bit of Chinese Five Spice powder? Lovely with the plums and it's also divine in cherry pie...

Just to follow up, I successfully made oven roasted peach preserves last night. Took about 2 1/2 hours. Started on 350 but ended up cranking to 450 about midway. Worked so wonderfully... And much less messy than on the stove top. I think this may be my go-to method now.

Mmmm... ESL, looks and sounds great! FWIW, I do a plum-cardamom which is really wonderful, as well as a ginger peach (using tiny nuggests of candied ginger). Truly yummy!

Here is a picture of a batch of rhubarb plum preserve from last year...

I have done many batches of plum preserves over the years. We have a tree that produces every 2 or 3 years. I prefer a wide baking pan or turkey roaster to a dutch oven, just because it has more surface area and will reduce quicker. I cook at 350-degrees and keep an eye on it, as they are juicier when more ripe and take a bit longer. Since each batch is so different, I usually let it go for 30 minutes to an hour at first, stirring every 20 minutes or so, then as it thickens, stir more often to keep the edges from browning. I then put it up just the same, into hot sterilized jars. I also do a batch with a cinnamon stick (removing it before canning) for a soft cinnamony flavor and no brown flecks like the cinnamon powder leaves.