1) Preheat your oven to 300°F. Line an 8" round cake pan with parchment (or foil), and grease the parchment.
2) Toast the hazelnuts and almonds for 20 minutes, until they're a light golden brown. It's best to do this in separate pans, as they toast at slightly different rates, and you may want to take one pan out of the oven before the other. Remove the nuts from the oven, and set them aside to cool a bit. When you can handle them, chop them coarsely.
3) Put the nuts, candied peel, spices, salt, and flour in a mixing bowl. Stir to combine.
4) Combine the sugar, honey, and butter in a saucepan. Over medium heat, bring the mixture to a boil. Using an instant-read or candy thermometer, boil the syrup, stirring frequently, till it reaches a temperature of about 245°F. This happens very quickly, so don't walk away; it should take about 2 minutes (or less) from the time the syrup starts to boil.
5) Immediately pour the boiling syrup over the fruit and nuts in the bowl. Stir to combine, and pour into the prepared pan, smoothing the top with a spatula (or your wet fingers; it cools down quickly, and you shouldn't find it overly hot). You need to work fast, as the mixture will start to stiffen up. Place the cake pan on a baking sheet, to catch any potential spills.
6) Bake the cake for 40 to 45 minutes; it won't seem firm, but will set as it cools. Remove it from the oven, and after 45 minutes, loosen the edges with a table knife or heat-proof spatula. Turn the warm panforte out of the pan onto a piece of parchment or foil. The bottom is now the top.
7) Sprinkle the top of the panforte heavily with confectioners' sugar, gently rubbing it in, if desired. Let it cool completely before wrapping airtight.
8) Store the panforte, at room temperature, for up to 2 months. To serve this rich cake, cut it in thin wedges.
Yield: about 20 servings.
To make chocolate panforte: Add 2 tablespoons Dutch-process cocoa to the nuts/peel/flour mixture. Melt 1/2 cup semisweet or bittersweet chocolate chips; stir them into the nuts/peel/flour along with the honey syrup. Bake as directed in the original recipe.