I made a try of creme patissiere with 250 ml UHT milk at 1.5% fat (yes, hence I called it a try), two egg yolks, 22g corn starch, 70g sugar and vanilla. Direction as classic. Beat yolks with vanilla seeds and sugar, add starch. Meanwhile warm the milk and the vanilla bean and just before boiling add a part of it to the yolk mixture and stir; add more and then move everything back to the heat and stir until thick. Cool down in an ice bain marie. Let it sit at room temp with either film on the surface or a sprinkle of granulated sugar.
After less than an hour at room temp, I notice that the product is no longer creamy, became too solid and took the shape of the container. Far away from a cream. Can it be due to the lack of fat in the milk, it being UHT or too much time on the heat?