To toast hazelnuts: Preheat oven to 350 degrees. Place 1 pound of shelled hazelnuts on a baking sheet and toast for 10 to 15 minutes. Remove from the oven and rub in a towel to remove the brown skins. Grease and flour two cookie sheets. Mix the dry ingredients, including the hazelnuts, in food processor. Add butter and pulse in a food processor just until the mixture is crumbly. Mix the eggs and liqueur in a small bowl, then add slowly to the dry ingredients, until they form a dough. Remove the dough from the bowl and place it on a lightly floured surface. Knead slightly and form into four, 1 1⁄2-inch-wide logs. Place on 2 cookie sheets. Bake at 350 degrees about 15 minutes, until firm to the touch. Cool the logs on racks, then cut them into 3⁄4-inch-diagonal pieces and place them, cut side down, on the cookie sheets. Return them to the 350-degree oven and bake 10 minutes, turn, then bake 10 more minutes. Cool on a rack. Melt the white chocolate in the microwave on high for 45 to 60 seconds. Stir with a fork and drizzle over the top crusts of the biscotti. Cool, then store in an airtight container.