Chicken thighs baked on a celeriac, carrot and onion base

An experiment. I had a large celeriac in the fridge and wondered how I could use this with the chicken. So:

4 chicken thighs

1/4 celeriac, peeled and cut into chunks about 1"x2"

1 large carrot, peeled

1 large onion, peeled and cut into chunks

balsamic vinegar, 1 tbsp

honey, 1 tbsp

white wine vinegar, 1 tbsp

vegetable oil 1tbsp

I put all the veg in a rectangular pottery dish and mixed in the honey, balsamic vinegar, white wine vinegar, oil, and salt and pepper. Once I flattened the vegetable layer, I put the lightly oiled chicken pieces on top, skin side up. Then I put the dish in the oven at 180C for 40 minutes. The chicken was nicely cooked and browned. However, the veg were still too crunchy. I took the chicken off the top and kept it warm. I covered the dish with cling film and put it on high in the microwave for 10 minutes. If I did this again, I would parboil the veg for 10 minutes, before putting them in the dish and proceeding as before. The result was a slightly tangy and sweet flavoured vegetable.