Preheat the oven to 350°. Lightly oil a baking sheet. On another rimmed baking sheet, toast the hazelnuts for 8 minutes, or until fragrant and golden brown. Let them cool, then rub the hazelnuts in a kitchen towel to remove the skins.
In a medium skillet, sprinkle the hazelnuts with 1/4 cup of the sugar. Cook over moderate heat, without stirring, until the sugar melts and browns, about 2 minutes. Stir to coat the hazelnuts with the caramel and scrape out onto the oiled baking sheet. Let the hazelnuts cool and harden, then break them into pieces. Reserve 10 whole hazelnuts for garnish. Transfer the rest of the nuts to a food processor and grind them to a coarse powder.
In a small bowl, dissolve the instant espresso in the water. In a large, stainless steel bowl, beat the heavy cream until thickened. Add the remaining 2 tablespoons of sugar and the dissolved espresso and beat until soft peaks form. Refrigerate 1 cup of the whipped cream.
Put the coffee in a large shallow bowl. Moisten 12 of the ladyfingers in the coffee, lightly dipping each side, and arrange them side by side on the bottom of a 9-inch springform pan. Break a few of the ladyfingers if necessary to completely cover the bottom of the pan. Spread one-fourth of the espresso whipped cream over the ladyfingers and sprinkle with one-fourth of the hazelnut praline. Repeat with the remaining ladyfingers, whipped cream and praline. Refrigerate the cake until firm, about 1 hour.
Warm a thin knife under hot water and run it around the inside of the ring of the springform pan. Remove the ring. Using a spatula, spread the reserved 1 cup of espresso whipped cream around the top and side of the cake. Garnish with the reserved whole hazelnuts. Cut into wedges and serve.
The cake can be frozen for up to 2 days. Serve softened or partially thawed.