This version, a radically lightened version of English roly-poly, with a buttermilk biscuit dough, bakes until crisp and golden; it’s almost like a jam-filled cookie.
In a food processor or bowl, combine all of the dry ingredients; pulse or stir to combine well. Cut in the butter until crumbly. In a small cup or bowl, beat the buttermilk or yogurtmilk mixture with the egg and vanilla until smooth. Add to the flour mixture and pulse just until combined, no longer. (The dough can be made several hours in advance; flour lightly, wrap