Right, my current approach, which works fairly well, is to spend some time writing out a couple approaches and splitting them it out into coherent delegatable tasks. This results in a 2-3 page doc that I can check with other engineers and business stakeholders to be sure it does what we really want it to. It also means we notice if an assumption we made is untrue and we need to re-think the scope or approach of the project.
I’m just worried that at some point, somebody will come along and ask for an estimate and I’ll say I cannot give one and that this means I am not really a professional.