“ One blessing, with the essence of three -- the shorter form of the post-meal blessing, an abridgement of the full form.
The commandment to bless after meals appears in Deuteronomy, ch 8:
7 For YHVH your God is bringing you into a good land—a land with streams and pools of water, with springs flowing in the valleys and hills; 8 a land with wheat and barley, vines and fig trees, pomegranates, olive oil and honey; 9 a land where bread will not be scarce and you will lack nothing; a land where the rocks are iron and you can dig copper out of the hills. ”