With a pointed serrated knife (like a steak knife) and starting from the middle, cut down into the bun to make a spiral. In a bowl, cream together the butter, sugar cinnamon and cardamom. Using a spoon (so you don't accidentally rip into the bread), smear the butter mixture into the cuts of the spiral and all over the top and sides of the bun so it’s evenly covered. Put it on a plate and microwave for 30-40 seconds.

Meanwhile, break off a corner of the Ryvita and crumble it up into a rough rubble (saving the rest of the cracker to either make more, or just to eat later on). When the bun comes out of the microwave, sprinkle the Ryvita crumbs over the top. Let it cool while you make a coffee, then tuck in.