Scrub the fruit well. Place in a pot, cover with water, bring to a boil, reduce heat to simmer, cover and simmer for 2 hours, checking every once in a while to make sure the water hasn’t boiled off too much. Drain and when cool enough to handle, cut the fruit in half carefully, and remove all of the seeds (otherwise the cake will be bitter).

Preheat the oven to 350 degrees F. Grease and flour, or line with parchment, a 9-1/2- or 10-inch springform pan. Use matzo meal instead of flour if you are baking for Passover.

Put the fruit, skin and all, in a food processor fitted with the steel blade and puree. Measure out 1-1/4 cups.

Beat the eggs with the sugar and baking powder at medium-high speed until thick and lemon-colored. Add the ground almonds and mix well. Mix in the pulped orange at low speed, in two or three additions, beating for 20 seconds after each addition. Pour into the prepared pan.

Bake for 1 hour, until firm and a knife comes out clean. If the top begins to get too brown halfway through, cover loosely with foil.

Note: If making for Passover, if you want to eliminate the baking powder, beat the egg whites separately, and fold into the batter at the end.