Beat the soured cream with the eggs and vanilla extract in a separate bowl, and then pour the mixture into the saucepan. Whisk in the plain flour and bicarbonate of soda.
Pour the cake batter into the greased and lined tin and bake for 45 minutes to an hour. Leave to cool completely in the tin on a cooling rack, as it is quite a damp cake.
When the cake is cold, transfer it to a cake stand or a plate and leave whilst you make the icing. Lightly whip the cream cheese until smooth, sieve over the icing sugar and cornflour and then beat to combine.
Beat in the double cream until you have a spreadable consistency, making sure not to over whisk.
Spread the icing on the top of the cake so that you get a frosting which resembles a frothy Guinness top!