Fill a small pot halfway with water, and set a bowl on top (the bowl should not touch the water). On very low heat, melt the chocolate with the butter and halva, stirring until the mixture is smooth (you may also melt the chocolate in the microwave, stirring every 30 seconds). Set aside to cool.
In a bowl, beat the egg yolks with the sugar. Incorporate into the melted chocolate.
In a separate, stainless steel bowl, beat the egg whites and a pinch of salt until it forms soft peaks.
Gently stir ¼ of the egg white mixture into the chocolate mixture to loosen, then fold in the remaining egg white mixture until combined.
To prepare whiskey crema, using a hand mixer or a whisk, whip thickened cream, sugar, salt and whiskey together until stiff peaks form.
Divide the mousse among eight ramekins. Spoon whiskey crema over the mousse. Refrigerate for at least 30 minutes.
Top with some chocolate shavings and halva crumbs, and serve.
NOTE: Chocolate halva mousse with whiskey crema pairs well with a Chocolate Rob Roy cocktail.