How to Make It
Preheat oven to 325°. Spread the walnuts on a baking sheet and toast for 8 minutes; let cool to room temperature.
Heat the maple syrup in a 1 1/2-quart saucepan over moderately-high heat. When the syrup begins to boil, reduce the heat to moderate and continue to boil for 10 minutes, stirring occasionally with a metal spoon. Remove the syrup from the heat and immediately stir in the walnuts. Transfer the glazed walnuts to a rimmed baking sheet. Use the metal spoon to spread the walnuts evenly over one half of the baking sheet. Set aside.
Combine the sugar and lemon juice in a clean 3-quart saucepan. Whisk to combine; the sugar will resemble moist sand. Caramelize the sugar by heating it for about 10 minutes over moderately-high heat, stirring constantly with a wire whisk to break up any lumps. The sugar will become clear as it liquefies, then it will brown as it caramelizes. Remove the saucepan from the heat, add the unsweetened chocolate and stir until melted. Immediately and carefully pour the caramelized chocolate mixture over the walnuts, covering all the nuts. Let harden at room temperature for at least 30 minutes.
Invert the praline onto a clean, dry cutting boardit should pop right out of the baking sheet. Use a sharp serrated knife and a sawing motion to cut the praline into pieces. Store the praline in a tightly sealed plastic container until ready to devour.
Be sure to use pure maple syrup for this recipe and not the sapless imitation they give you at the pancake house.
You can use the pralines in other confections—try folding 1/4-inch pieces into white chocolate or vanilla ice cream.