I put less bicarb in (2 tsp) and it bubbled up fine, but I don't see how it should be causing enormous problems to use one Tbsp eiher. The key is to have a pan about 5 times the size of the amount of mixture - I remember making the mistake as a kid but being switched on enough to hold the pan over the prepared tray, and being a childI had oven gloves on the whole time. Not a mistake one makes twice either way.
I did the hard crack test (as I don't have a sugar thermometer) but it seems it wasn't quite done enough because though it's set solid, when I chew it I could easily lose a filling. My problem though, not the recipe. Sure the hard crack is the right stage, but it's less accurate than the thermometer in the end. I'll try stirring it into icecream so the cold helps stop it taking my fillings out