At my company, we always bond the aerated concrete with adhesive, super smooth. Then we plaster with regular plaster mortar. For an optimal surface, I recommend priming the entire aerated concrete surface with a thin layer of mortar, to later apply the final plaster. This is because aerated concrete absorbs the water from the mortar extremely quickly, so it will dry more evenly and smoothly if you do this. However, pre-wet in both steps.
