Sandwiches

A puzzle based on the 'spiral' principle, but this chain of linked answers is placed in a grid with a more regular design. In fact, the grid resembles two slices of white bread with a filling, hence the puzzle's name. The 'filling' (the middle row of shaded squares) is a spell-out – of a name or book title, perhaps. Guessing the spell-out from the letters already placed before the puzzle is complete will help the solver to crack the unsolved clues.