In a metal stand mixer bowl, combine the eggs and granulated sugar. Beat well to combine. Place the bowl on top of a small pot with 1-inch of boiling water; be sure that the bowl does not touch the water. Beat the eggs until they have tripled in size and the whisk leaves a trail, 5 to 7 minutes.
Once the eggs have tripled in size, remove the bowl from the double boiler and put on the stand mixer equipped with the whisk and beat on a medium speed until the bottom of the bowl feels cool, about 5 minutes. Add the mascarpone and chocolate chips and mix until just combined. Refrigerate 1 hour.
When the espresso mixture has cooled, dip the cookies in the liquid one at a time and line the bottom of a 9 by 13-inch baking dish. Spread 1/3 of the chilled mascarpone mixture over the cookies. Repeat this process 2 more times finishing with a layer of mascarpone. For more stability, lay the second layer of cookies in the opposite direction of the first layer.
Cover and refrigerate for at least a couple of hours and up to overnight; the longer it chills the easier it will be to slice.
Top the tiramisu with finely grated chocolate. Cut into squares and serve.
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