Make the praline:
Lightly oil a heavy-duty rimmed baking sheet. Put the sugar and 1/4 cup water in a heavy-duty 3-quart saucepan or sauté pan and cook over medium-high heat, stirring, until the sugar dissolves, 1 to 2 minutes. Let the mixture continue to cook without stirring until it’s a medium amber color, about 5 minutes more.
Carefully add the hazelnuts—don’t let the hot caramel splash you. Continue to cook, swirling the pan gently to coat the nuts, until the caramel is deep amber, 1 to 2 minutes more. Carefully pour the praline onto the prepared baking sheet and let cool completely.
Break the praline into pieces by smacking it on the counter or cracking it with a rolling pin. Put the pieces in a food processor, add 1/2 tsp. salt, and pulse to form a coarse powder. If you end up with a few large pieces but the rest is the right texture, remove them, dump out the powder and process again. Set aside.
Make the fillings:
In a small bowl, stir the espresso powder into 1 Tbs. of the crème fraîche until dissolved.
In a large bowl, whisk the mascarpone and the confectioners’ sugar until blended.
In a medium bowl with an electric hand mixer, beat the remaining crème fraîche on medium speed until soft peaks form, about 2 minutes. With a rubber spatula or big spoon, gently fold half the whipped crème fraîche into the mascarpone mixture until smooth, then fold in the second half.
Put 1-1/2 cups of the mascarpone mixture in a bowl. Gently fold in 1-1/4 cups of the praline powder. Gently fold the espresso-cream into the remaining mascarpone mixture.
Assemble the crêpe cake:
Lay 1 of the crêpes on a flat cake plate or platter that’s at least 9 inches in diameter. Spread a generous 1/4 cup of the espresso filling evenly over the crêpe, leaving a 1/4-inch border. Lay a second crêpe on top. Spread a generous 1/4 cup of the praline filling evenly over the crêpe, leaving the same border. Continue alternating the espresso and praline fillings until you’ve used all the crêpes. To avoid a “domed” cake, make the depth of the cream around the edges of the crêpes a touch deeper than in the centers, and when you add a new crêpe, lightly press down on the center of it with your fingers. Finish with a thin, even layer of the praline cream.
Carefully wrap the cake in plastic and chill for at least 4 hours or up to 24 hours. The fillings will set up slightly, making the cake easier to slice.
Remove the cake from the refrigerator at least 1 hour before serving. Sprinkle the remaining 1/4 cup praline powder on top and dust with confectioners’ sugar.
nutrition information (per serving):
Photo: Scott Phillips