Combine all ingredients, except Peychaud's bitters and soda water, in a cocktail shaker and shake well. Add ice and shake again. Strain into a martini glass. Set aside one half of the cocktail shaker, without ice, to save the film left from the cream and egg. In the shaker, add 2 dashes of Peychaud's Bitters and combining it with the left over film and add enough soda to create a foam. Top the drink with this foam until a head appears. Garnish with lemon zest.