Layers of pastry rising, wrapped in case of soya (6)
I believe the answer is:
strata
'layers' is the definition.
(stratum is a kind of layer)
'pastry rising wrapped in case of soya' is the wordplay.
'pastry' becomes 'tart' (tart is a kind of pastry**).
'rising' says the letters should be written in reverse (going up in a down clue).
'wrapped in' indicates putting letters inside.
'case of' means to remove the middle letters (outsides of).
'soya' with its middle taken out is 'sa'.
'tart' backwards is 'trat'.
'trat' inserted within 'sa' is 'STRATA'.
'of' is the link.
(Other definitions for strata that I've seen before include "hard beds" , "Layers into which rocks are divided" , "Layers as of rocks in earth's crust" , "Geological levels" , "Geological layers" .)