Complex sentence: Constitutionally, the Prime Minister and the cabinet are responsible to the monarch, not the Cortes, and the monarch may nominate anyone he sees fit as his prerogative to form a government.
Split into simpler sentences: Constitutionally, the Prime Minister and the cabinet are responsible to the monarch, not the Cortes. On paper, the monarch is free to name anyone he sees fit as his prerogative to form a government.