I need a bit of reasonably urgent advice, please. I am planning on making a chicken thigh dish tonight that I have made only once before. It is an easy and tasty dish. I need to sauté red onions and garlic and add to that one cup of chicken stock and balsamic vinegar. The chicken thighs are placed on top with pesto and Parmesan spread over them. They get baked in the oven, covered, for a time and then baked uncovered. I found that the sauce was very thin and I would love to improve on it.
Should I bake the dish uncovered from the start perhaps so that there is some evaporation or should I mix a little butter with flour and drop that in to thicken or is there another easy way to overcome the problem? Thank you for your suggestions.

I would bake it uncovered, keeping an eye on it in case it gets too dry. The alternative would be to bake it according to the instructions, then remove the pieces of chicken and keep warm while reducing the remaining liquid at a fast boil. Again, watch it carefully.

Beurre manie (butter and flour mixture) works quite well but only if you can incorporate it quickly by whisking it in, so you would have to remove the chicken pieces to do that. I used to use it when we ate flour, but these days I thicken by reduction and I prefer the concentrated flavour that ensues.

I usually add a slurp of very good olive oil or a lump of butter to a reduced sauce just before serving; it smooths the texture and gives depth of flavour.

As per TPANDAV I'd probably cook it without covering. Or cover it but use less stock, and reserve further stock if needed, to be added during the uncovered cooking time. Sounds very tasty.

Thank you TPANDAV and Griz. I will be baking uncovered and keep an eye on it. Because a couple of friends will be joining us for dinner tonight I don’t want to make things more difficult.

I baked the chicken uncovered and it made some difference to the quantity of the sauce but not as much as I thought. Next time I’ll reduce the chicken stock. I think there is a fair amount of moisture coming out of the oregano and parsley pesto. . It turned out a tasty dish that I will make again.

I often use a slurry of cornflour and water to thicken a sauce, especially one that has larger "bits" in it such as a casserole or in this case your baked chicken and veges. It's a less sophisticated result than reduction or butter but it doesn't add any extra fat and its fast and very easy to add a little at a time to get the desired thickness to your sauce. Less is often more in this case and you will probably find you only want to give that little bit of shine and viscosity rather than a gravy but either way it just a matter of adding until you are happy because it thickens straight away. Take your dish off the direct heat and mix well as you add it to avoid lumps. This way you will still have plenty of sauce! You can remove your chicken pieces until you are happy with the sauce them put them back on top.

Good advice Danube. Thank you.