Cut 3 carrots into 1/2-inch-thick rounds. Place a steamer basket in a medium saucepan containing 1 inch of water. Bring water to a boil; add carrots. Steam until fork-tender, about 10 minutes. Transfer to a medium bowl, and mash with a fork to yield 1 cup; set aside. Grate the remaining 2 carrots to yield 1 cup, and set aside.
Preheat the oven to 350 degrees. Grease an 8-inch-round Bundt or angel-food cake pan with margarine, and dust with matzo meal. In a small bowl, whisk together 1/3 cup potato starch, ground pecans, cinnamon, and allspice; set aside.
In the bowl of an electric mixer fitted with the whisk attachment, beat all 4 egg yolks and brown sugar on medium-high speed until mixture holds a ribbonlike trail on the surface for 3 seconds when you raise the whisk. Add mashed carrots, orange zest, and margarine. Continue beating until mixture is light in color. Transfer to a large bowl. Wash and dry mixer bowl and attachment.
Place egg whites in the mixer bowl, and beat on medium-high speed until soft peaks form. With the mixer running, slowly pour in the superfine sugar, and beat until stiff and glossy. Fold both the egg-white and potato-starch mixtures into the egg-yolk mixture. Fold in raisins, chopped pecans, and grated carrots. Pour batter into the prepared pan.
Transfer pan to oven; bake until a cake tester inserted into the middle of the cake comes out clean, about 40 minutes. Transfer pan to a wire rack to cool, about 2 hours.
To unmold the cake, hold the pan in a hot-water bath for 10 seconds, then invert the cake onto a serving platter. Place granulated sugar and remaining 1/2 teaspoon potato starch in the bowl of a food processor. Process 2 minutes. Before removing the lid of the bowl, let dust settle. Transfer mixture to a fine sieve, and dust cake.