The unclued lights (one of two words and another hyphened) can be arranged to form a word pyramid of 3 to 11 letters, adding one letter and making an anagram step by step.
 

Across

 
11    Demands performances from the past? (6)
13    Totally obsessed having cleared the plate (7, two words)
15    Land where heated bath’s popular (5)
16    Recent cut in coffee (5)
17    Open unusual Scottish rucksack outside (6)
18    Tipsy round rear of shop (5)
20    One who reported home (6)
21    Passageway in centre of Scottish burgh (5)
22    Dog having baked beans — just ideal for...