Set to launch towards the end of next month on Dirty Lane, Longboys Borough Yard will have 45 covers split across two floors, with counter dining at ground level.
The opening will roughly coincide with the launch of a grab-and-go version of Hornigold's finger doughnut brand in Liverpool Street.
The new openings will bring the group - which was founded in 2019 - up to a total of four sites, joining the flagship Longboys in Coal Drops Yard and a site in Boxpark Wembley.
The brand’s products are also stocked in Harrods and Selfridges.
Specialising in the eponymous éclair-doughnut hybrid, Longboys is billed as the first and only dedicated finger doughnut brand in London.
All doughnuts are hand-rolled fresh, every day in small batches, to create a light brioche base filled with compotes, fillings, glazes, and toppings, all carefully made in house.
Using only the ‘finest seasonal ingredients’, both sites will offer the new autumn range of flavours, including Sticky Toffee Pudding, Coconut Chocolate, Vanilla Malt and Apple Crumble.