Separate the egg whites and egg yolks. In a the bowl of a stand mixer with whisk attachment or in a large bowl with a hand held electric beater mix the egg yolks and vanilla extract on low until combined.
Add the sifted icing sugar and beat on low to combine then high until mixture is creamy and has lightened in colour. Scrape down the sides of the bowl and beat again briefly. Add the whipping cream and beat on low again to combine and then beat on high until the icing sugar is well dissolved. Mix in the vodka and lemon juice on low until combined.
Pour mixture into a clean, one litre mason jar and close the lid tightly. Shake the jar every few days. Although it's tasty right away, the flavours develop and the mixture becomes a delectable, smooth liqueur after about two weeks.
Store in the fridge and it will keep for months (but I doubt it will last that long!).