Pastry Sour Beers are a modern twist on a Kettle Sour. With the use of additional sugar (often lactose), they are sweetened and creamy. This creates a dessert-like flavour. This is why they are known as a 'Pastry' Sour.
Brewers have been taking this one step further, using other sweet ingredients to create playful dessert-flavoured sour beers.