While the polenta was cooling I went on to make the balsamic reduction. Which meant - more constant stirring! This recipe is so easy and pretty fool-proof. Just pour, into a small saucepan, an amount of vinegar which is double the amount of sauce you want to end up with. Put the heat on high and whisk, whisk, whisk. Keep whisking until the sauce is reduced by at least half and has a syrupy consistency (I was a bit unsure about when to pull it off the heat and then - poof! - it was suddenly right). If you would like to make it a bit sweeter, add a bit of sugar while it's cooking. The sugar made it yummy but I think it altered the texture to be a bit taffy-like when cooled.
By now your polenta should have moulded into the shape of your container. I cut some slices out, sprayed a pan with cooking oil and cooked them for about 20 minutes, flipping once the bottom was a golden brown.
They can cook for a while without burning, so just cook them until you they reach your desired crispiness. Plate with a generous drizzle of balsamic reduction and some cooked veggies.