I have used both chefsteps and jacques pepin recipe for the creme brulee (i mean ingredients) then i put them in aluminium ramekins and put them in a tray with 3/4 water .. my problem is by the time they bake outside , at the centre they are still liquid... i bake them at aprox 170 celsius for 30'. At home i get them perfectly but at the restaurant no .. please explain this

thank you