Anh Tuan, 32, co-owner of the cafe in Thuan Hoa Ward, said the idea came from a desire to showcase Hue's culinary traditions while offering something different.
Hue is already known for salt coffee, prompting the team to explore another distinctive local ingredient. They eventually chose mam ruoc, widely used in Hue cooking but rarely found in drinks.
The idea was initially dismissed as impractical, but after experimenting with the combination, the team found the flavours worked well together and spent about six months refining the recipe.
The mam ruoc used for the drink must have a distinct salty flavour without any sourness, which could affect the cream. To soften its strong aroma and saltiness, it is cooked with caramelised sugar and cream, with only a small amount used in each serving.
The finished drink has four layers, with fresh and condensed milk at the bottom, followed by espresso, a creamy mam ruoc sauce and thinly shaved dried tuna on top.
Customers are advised to sip directly from the glass rather than stir the drink or use a straw, allowing them to taste each layer more clearly.
Thu Uyen, a Hue resident who tried the drink after seeing it discussed on social media, said the mam ruoc aroma was milder than expected and the combination of milk, coffee and mam ruoc made for an interesting experience.
She said sipping the drink allowed her to better taste the different flavours and described it as an experience worth trying.
Videos featuring the drink have attracted tens of thousands of views on social media, with many users expressing curiosity about trying it.
Priced at VND 55,000 (USD 2.10) per glass, mam ruoc coffee has turned an idea once considered impractical into an unusual take on Hue's local flavours.