the answer is... Hylotelephium 'matrona' (syn. sedum)

Recently renamed 'hylotelephium' - having enjoyed simply being 'sedum' before, this amenable perennial grows from a rosette of fleshy green leaves in spring, sending up elegant stems bearing a flat-topped flower cluster. These mature from white buds into pale pink summer flowers to become a rich red in autumn. Seedheads stand well over winter and look very elegant traced in frost. Plants can flop int eh middle in fertile clay soils but giving them the 'Chelsea Chop' in late May can prevent this, though they will flower later. A good plant for seasonal interest in a sunny border. H and S45cm (18in)