This is a very heavy, dense “cake” that keeps well for months. It can be served in tiny slivers on its own, but we love it served with a cheese plate.
Preheat the oven to 300°F. Butter the bottom and sides of a 10-inch round springform pan and line the bottom of the pan with:
Toast:
Add to a food processor and pulse until the nuts are coarsely chopped. Transfer to a medium heatproof bowl and add:
Stir until well mixed. Combine in a small heavy saucepan:
Stir over medium-low heat until the sugar is dissolved, about 5 minutes. Increase the heat to medium-high and bring the mixture to a boil. Cook until it reaches the firm-ball stage, 245° to 248°F (for details on this step, see here). Quickly pour the syrup over the dry ingredients and stir with a wooden spoon until completely coated. Transfer the mixture to the prepared pan. Dampen your fingertips, then press evenly into the pan and smooth the top. Bake for 35 minutes. The panforte may not look set, but it will firm as it cools. Cool completely in the pan on a rack. Run a thin, sharp knife around the edge of the pan, then carefully remove the sides of the springform. Dust heavily with:
Cut into very thin slices or store, tightly wrapped, at room temperature, until ready to use.