Combine the type 00 flour, hazelnut flour, icing sugar, ground coffee, and cold unsalted butter in a mixing bowl. Rub the mixture between your fingers until it resembles coarse crumbs.

Add the egg, 15 ml espresso, and salt to the crumb mixture. Mix just until a uniform dough forms.

Flatten the dough into a disc between two sheets of parchment paper. Roll it to a 3 mm thickness.

Refrigerate the rolled dough for at least 120 min. Keep it flat between the parchment sheets.

Line the 22 cm perforated tart ring with the chilled dough. Trim the excess pastry neatly.

Freeze the lined tart shell for 30 min. Bake it at 160°C / 320°F for 25 min until set and lightly golden.

Finely chop the gianduja chocolate and place it in a heatproof mixing bowl. Heat 80 ml of the heavy cream until it reaches a boil.

Pour the hot cream over the gianduja chocolate. Whisk until the ganache is glossy and smooth.

Pour the gianduja ganache into the cooled tart shell. Let it cool until the surface begins to set.

Cut the panettone into a 1 cm thick layer sized to fit the tart. Place the panettone over the cooled ganache.

Soak the gelatin sheets in cold water until softened. Squeeze out the excess water.

Heat the whole milk, remaining 90 ml heavy cream, honey, 30 ml espresso, and instant coffee in a saucepan. Stir until the instant coffee dissolves.

Remove the coffee mixture from the heat and add the softened gelatin sheets. Stir until the gelatin completely dissolves.

Melt the white chocolate and place it in a tall mixing bowl. Pour the warm coffee mixture over the melted white chocolate.

Add the room-temperature mascarpone to the coffee-chocolate mixture. Blend with the immersion blender held at the bottom until perfectly smooth.

Pour part of the coffee mascarpone cream into the quenelle mold. Freeze the molded cream until firm enough to unmold.

Pour the remaining coffee mascarpone cream over the panettone layer. Refrigerate the tart for at least 180 min until set.

Unmold the frozen cream quenelles and arrange them on the chilled tart. Dust the tart lightly with cocoa powder before serving.