Preheat the oven to 350°F. Line two large baking sheets with parchment paper.
Combine the flour, sugar, cocoa, espresso powder, baking soda, and salt in the bowl of an electric mixer. Mix for 30 seconds on low speed to combine. Add the hazelnuts and chocolate chips and mix well.
In another bowl, lightly beat the eggs with the vanilla. On low speed, pour the eggs into the dry ingredients and mix just to form a soft dough.
Divide the dough into 4 equal pieces. On a lightly floured work surface, roll each piece under your palms into a 14-inch cylinder about 2 inches in diameter. Transfer to the prepared baking sheets, placing 2 logs on each baking sheet, about 2 inches apart.
Bake for about 30 minutes, until the logs are lightly browned and firm. Let cool completely on the baking sheets on wire racks. Reduce the oven temperature to 300°F.
Transfer one of the cooled logs to a cutting board. With a heavy sharp knife, cut the log into 3/4-inch-thick slices. If sliced crosswise, each log will average 24 small cookies. If cut on an angle, each log will yield about 16 large pieces. Repeat with the remaining logs. Spread the cookies on the parchment-lined sheets.
Bake the cookies for 30 minutes, turning halfway through baking, until crisp. Transfer the cookies to wire racks and cool completely.
Place the white chocolate in the top of a double boiler or metal bowl over simmering water and melt, stirring occasionally. Remove from the heat. Dip each cooled cookie halfway down into the melted chocolate, scraping off the excess chocolate against the rim of the bowl. Place the dipped cookies on a sheet of parchment or waxed paper and let cool until the chocolate sets.
Yield: about 64 large or 96 small cookies