personally when I say heaped teaspoon I mean slightly more than a teaspoon (5ml) but not as much as a dessertspoon (10ml) - it's not that precise as i don't weigh the ingredients out or level the spoons, if you want to say rounded teaspoon feel free - i'm just using a basic set of measuring spoons (1/4 tsp, 1/2 tsp, 1 tsp, 1 dsp, 1 tbsp). I don't think it has to be that precise, as alluded to above, your heaped/rounded spoons by eye may be different to mine. As long as the ratio is the same I can't see it being that critical to the overall result, at least in this recipe.