Cake made with breadcrumbs rather than flour might seem odd, but doesn’t taste it. This is a cake for morning coffee or afternoon tea in smallish slices rather than a dessert.
Melt the chocolate. There is no way to do this quickly. Break the chocolate into small pieces, place them in a bowl and stand the bowl in a pan of warm water. Alternatively leave the chocolate somewhere warm in the kitchen and be patient.
Cream the butter and caster sugar together until pale.