From the story Cuisine in Translation

Matzo
½ lb fine suet
6 apples thinly sliced
Sugar
Raisins
Cinnamon
Almonds
Yolks of 7 eggs
Whites beaten

Bake one hour.

Note: What Aunt Bebette assumes we would know is that the matzos should be soaked and then squeezed of excess water. The egg yolks should be mixed with the sugar and cinnamon, and then the suet, matzos, raisins, almonds and apples are mixed in. The beaten egg whites would be folded into the mixture before it is placed in a baking dish and baked for 1 hour at 325 degrees
Suet is raw, uncooked, beef or mutton fat, especially the hard fat found around the loins and kidneys. It melts at about 70°F. The primary use of suet is to make tallow in a process called rendering, which involves melting and extended simmering, followed by straining and cooling. You might substitute butter in this recipe, however, the dish would no longer be kosher for Passover.