Start by making the crêpe batter. Melt the butter and set aside. Crack the eggs into a bowl and beat them with a fork. Sift the flour into a large bowl or the bowl of your stand mixer, then add the salt and sugar.

Pour in half of the milk and mix. While continuing to mix, gradually add the beaten eggs, then the melted butter and oil. Finally, slowly add the remaining milk.

For an extra smooth batter, strain it through a sieve. Let the batter rest for at least 1 hour. Cook the crêpes in a well-oiled, hot nonstick skillet. Place the crêpes on a plate, cover with plastic wrap, and let cool.

Prepare the chocolate mousse. Melt the chocolate in a double boiler. Heat the milk in the microwave to 140°F (60°C), then add it to the melted chocolate in three additions, mixing well each time.
Using a stand mixer, whip the very cold heavy cream until stiff peaks form, then gently fold it into the chocolate mixture with a spatula. Transfer the mousse to a piping bag and set aside.

Line a loaf pan with parchment paper or plastic wrap. Begin assembling the cake. Place 2 crêpes slightly overlapping, then trim the edges so they fit the length of your loaf pan and even out a third side. Using a spatula, spread a thin layer of chocolate mousse over the entire surface.

Roll them up lengthwise, starting from the right edge. Place the roll in the pan. Repeat this process to fill the bottom of the pan. Then spread about a 1/2-inch (1 cm) layer of chocolate mousse. Make more crêpe rolls for a second layer, then add another layer of mousse.

When you reach near the top of the pan, alternate leftover crêpe pieces and mousse, finishing with a whole crêpe layer. Cover the top and freeze for 30 minutes.

Meanwhile, make the smoothing ganache. In a saucepan, heat the cream and honey to a boil, then pour over the chocolate in three additions, mixing well each time.

Unmold the cake onto a wire rack set over a deep dish. Using a spatula, spread the ganache over all surfaces to fill any gaps. Then pour the hazelnut crunch glaze over the cake. The glaze should be between 86°F and 95°F (30°–35°C). Chill for at least 30 minutes to set the glaze. Let sit at room temperature for 15–20 minutes before serving!