Beni Imo Tarte

the signature pastry of Okinawa: a butter-rich shortcrust shell filled with a smooth, vivid-violet cream of Okinawan purple sweet potato and cream cheese, baked until just set, the beni imo tarte is the most distinctive regional baked good in Japan

Origin: The Ryūkyū Kingdom — Okinawa and the Southern Islands

From the journey of Sweet Potato.

The Okinawan purple sweet potato (beni imo, literally 'red-purple potato') was selected over centuries by Ryūkyūan farmers from the orange-fleshed sweet potato introduced from Fujian by Noguni Soukan in 1605 and possibly from additional introductions through the VOC's Japanese trade at Nagasaki. Through sustained selection for the Ryūkyū chain's particular soil and climate conditions, farmers identified and propagated varieties with an unusually high concentration of anthocyanin pigments that give the cooked flesh an intensely vivid violet-purple colour quite unlike anything in the orange-fleshed mainland Japanese tradition. The beni imo tarte as a commercial product was developed in the 1980s by a confectionery company based in Naha and has become one of the most recognised regional souvenir foods in Japan; visitors to Okinawa bring it home as a gift, and its packaging (white cardboard boxes with the unmistakably violet filling visible through a cut-out window) is one of the most familiar sights in Okinawan airports. The tarte is small, individual-sized, and precisely moulded: a deep, fluted shortcrust case pressed to an even thinness and filled with the purple sweet potato and cream cheese filling to a level surface, then baked until just set. The pairing of purple sweet potato with cream cheese produces a filling that is simultaneously sweet and slightly tangy, smooth and dense enough to hold its shape when cut, and so vividly coloured that it looks almost artificial, though the colour is entirely natural and, indeed, one of the highest concentrations of anthocyanins found in any common food plant.

Ingredients

Shortcrust Pastry

180 g plain flour
90 g cold unsalted butter, cut into small cubes
30 g icing sugar, sifted
1 egg yolk
2 tbsp cold water
1 pinch fine salt

Purple Sweet Potato Filling

400 g purple sweet potato (Okinawan beni imo or Stokes Purple variety), peeled and cut into chunks
200 g full-fat cream cheese, softened to room temperature
80 g icing sugar, sifted
2 eggs
60 ml double cream
1 tsp vanilla extract
1 pinch fine salt

Method

Make the pastry: rub the cold butter into the flour and icing sugar with your fingertips until the mixture resembles coarse breadcrumbs. Add the egg yolk, water, and salt and bring together into a dough with minimal handling. Flatten into a disc, wrap in cling film, and refrigerate for at least 1 hour.
Steam or boil the purple sweet potato chunks for 20–25 minutes until completely tender. Drain and allow to steam-dry for 5 minutes. Pass through a fine-mesh sieve or potato ricer while still warm to produce a smooth, lump-free purée. Allow to cool completely.
Preheat the oven to 180°C / 160°C fan. Roll out the chilled pastry on a lightly floured surface to 3 mm thickness. Line one 23 cm loose-bottomed tart tin or eight individual 8 cm fluted tart tins. Press the pastry firmly into the flutes and trim the top. Prick the base lightly with a fork. Blind-bake with baking beans for 12 minutes, remove the beans and bake for a further 5 minutes until the base is pale gold. Allow to cool slightly.
Beat the cream cheese until smooth and light. Add the cooled sweet potato purée and beat until fully combined and vividly coloured. Add the icing sugar, eggs, cream, vanilla, and salt. Beat until smooth and completely homogenous.
Pour the filling into the par-baked tart case(s), smoothing the surface level. Bake for 18–22 minutes until the filling is just set: it should have lost its raw jiggle but still have a very slight tremor at the very centre. Allow to cool completely in the tin before unmoulding.
Serve at room temperature or lightly chilled, unmoulded from the tin. The violet surface should be smooth and undisturbed.

Notes

Okinawan beni imo is the ideal; it can be sourced from Japanese grocery shops and specialist importers. The 'Stokes Purple' variety, now widely grown in California, is the best widely available substitute; it has a similarly intense pigmentation and slightly sweeter flavour. The purple of the filling is entirely natural and is caused by anthocyanins; it can be partially bleached by acids, so avoid adding lemon juice to this filling. The tarte keeps well, covered and refrigerated, for 3 days.

The Gastrographer

Name: Beni Imo Tarte
Prep time: 30 min
Cook time: 30 min
Total time: 2 h
Yield: 8
Cuisine: The Ryūkyū Kingdom — Okinawa and the Southern Islands
Ingredients: 180 g plain flour; 90 g cold unsalted butter, cut into small cubes; 30 g icing sugar, sifted; 1 egg yolk; 2 tbsp cold water; 1 pinch fine salt; 400 g purple sweet potato (Okinawan beni imo or Stokes Purple variety), peeled and cut into chunks; 200 g full-fat cream cheese, softened to room temperature; 80 g icing sugar, sifted; 2 eggs; 60 ml double cream; 1 tsp vanilla extract; 1 pinch fine salt

Mapping Culinary History

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Journey Point Map Key

Ingredient originTrade or transit route

Became a culinary stapleColonial / trade control