Whisk the egg yolks, 1/4 cup of sugar, butter, 1/4 cup of water, coffee liqueur, and chili oil in a large metal bowl to blend. Set the bowl over a saucepan of simmering water (do not allow the bottom of the bowl to touch the water); whisk constantly until the mixture is very thick and frothy, about 3 minutes. Add the chocolate and stir until melted and smooth. Remove from the heat.
Using an electric mixer, beat the egg whites in another large bowl to soft peaks. Gradually add the remaining 1/4 cup of sugar, beating until stiff and glossy peaks form. Remove the chocolate from over the water. Fold 1/3 of the meringue into the warm chocolate mixture to lighten, then fold in the remaining meringue.
Cover tightly with plastic wrap and refrigerate until set, at least 3 hours or overnight. Spoon the mousse into 6-ounce bowls. Top with spicy whipped cream and serve.
Combine the oil and crushed red pepper flakes in a heavy small saucepan. Cook over low heat until a thermometer inserted into the oil registers 180 degrees F, about 5 minutes.
Remove from heat. Cool to room temperature, about 2 hours. Transfer the oil and pepper flakes to a 4-ounce bottle. Seal the lid. Refrigerate up to 1 month.
With an electric mixer, whip cream gradually adding the sugar until soft peaks form. Top with a dusting of cocoa powder and a pinch of cayenne. Serve immediately.
Consumption of raw or undercooked eggs, shellfish and meat may increase the risk of foodborne illness.