Preheat the oven to 350°F. Coarsely chop the hazelnuts. In a bowl, combine the nuts, sugar, butter, liqueur and eggs and mix well.

Stir in the flour, baking powder and salt. Turn the dough out onto a floured surface and knead briefly; then form into a long loaf about 2 inches wide. Place the loaf on a parchment-lined or lightly oiled cookie sheet and bake in the middle of the oven for 25 minutes or until firm. The loaf will have a cakelike texture. Remove from the oven and cool.

Cut the loaf diagonally into 1/2-inch slices and lay these out on a cookie sheet. Bake for 20 minutes more, turning them once until both sides are lightly browned and toasted. Cool and store in an airtight container.