Preheat the oven to 400° and line 2 large rimmed baking sheets with parchment paper.
Spread the hazelnuts in a pie plate and toast until the skins split and the nuts are fragrant, about 10 minutes. Transfer to a clean kitchen towel and rub together to release the skins. Let the hazelnuts cool completely.
In a food processor, pulse the hazelnuts until finely chopped. In a medium bowl, using a hand mixer, beat the egg whites with the salt at medium speed until foamy, 2 minutes. Gradually add the sugar and continue beating until soft peaks form when the beaters are lifted, 5 to 7 minutes. Fold in the hazelnuts.
Using a 1-ounce ice cream scoop or a soup spoon, scoop 1 1/2-inch rounds of the batter onto the prepared baking sheets, about 1 inch apart. Bake the cookies for 11 to 13 minutes, until fragrant and lightly browned; rotate the baking sheets from top to bottom and front to back halfway through baking. Remove the cookies from the oven and, while they’re still hot, carefully make an indentation in the center of each with the back of a teaspoon.
In a small saucepan, boil the raspberry jam for 30 seconds, until slightly thickened. Carefully spoon about 1 teaspoon of the hot jam into the center of each cookie. Let the jam set and the cookies cool completely before serving.
In a microwave-safe bowl, heat the chocolate at high power in 30-second bursts until just melted. Stir until smooth. Dip the top of each sandwich cookie in the chocolate, just enough to coat the almond paste; transfer to the baking sheet. Top each cookie with a walnut half. Let the chocolate set before serving.
The cookies can be stored at room temperature in an airtight container between wax paper for up to 4 days.