Nigel Slater's Marsala Almond Chocolate Slice

I came across this luscious cake via an Instagram post by Nigella Lawson, which linked to the recipe by Nigel Slater. I felt it was my duty to make it; maybe yours, too. It’s truly a slice of heaven, a bit like Torta Caprese (the chocolate-almond torte from Capri) but baked in a loaf pan and cut into slices rather than wedges. I made it three days ago a…