Not really a "skill" as such, but oven temperatures just annoy me! I know that different types of ovens heat and distribute heat differently (fan assisted, gas, electric etc), but it seems no matter WHAT recipe and what oven i'm using (and i've had many different types), I always seem to have to take about 10-30'C off of the temperature they give in the recipe.
Made a basic sponge yesterday and it said 190C, but that caused it to brown way to quick, so i turned it down to about 180C.
I've got a temperature probe, I should probably see if my current oven is accurate at some point.. but yeah.... annoying