Heat oven to 350 degrees F and place a baking sheet on the middle shelf of the
Wash the cranberries and pat dry.
Thickly smear the butter on the base of a 9-inch round cake pan.
Add the sugar and swirl to coat evenly.
Add the walnuts if using, and spread evenly.
Add the cranberries and spread into an even layer.
For the batter, sift the flour and baking powder and set aside.
Combine the eggs, sugar and rind in a heatproof bowl over a pot of hot (not boiling)
With an electric mixer, beat until the eggs leave a "ribbon trail"
when the beaters are lifted.
Add the flour mixture gradually, folding in well after each addition.
Gently fold in the melted butter, then pour the batter over the cranberries.
Place pan on baking sheet in oven and bake for 40 minutes.
Allow to cool for 5 minutes in pan, then run a knife around the edge to loosen.
To unmold, place a large serving plate over the pan (while the cake is still warm).
Holding the plate and pan together, using potholders, flip over and carefully lift
the pan. If any cranberries, etc. are stuck to the pan, spoon off and place on the
cake wherever it appears to need it.