Pre-theatre dining. Three words that strike fear into discerning diners’ hearts. Images of the grey-matter pancakes Cote call ‘steak’ surface. Stained menus selling off lunch leftovers. Atmospheric black holes, devoid of soul or style. Heartburn that puts the prix in prix fixe. It’s all expensive, rushed, and underwhelming – an impression of dinner rather than the thing itself.

It is little wonder, therefore, that past reviewers of Lasdun, the National Theatre’s culinary offering, have extolled the virtues of the restaurant despite its setting, choosing to recommend it outside of showtime hours – as though the food succeeds in spite of the theatre.

On a rainy March evening, my friend Holly and I went to find out. Both Irish playwrights and actors, we wanted Lasdun to be an extension of the building that houses it: as dramatic, as ambitious, as classic and potentially delicious. We also needed to be fed in the hour and a half before the first act of Dear England – and leave richly satisfied while not so heavily sedated that we would make it to the second.

A good play often translates an audience elsewhere; out of time, place, season. And Lasdun delivered a knockout performance. At £40 for two courses, the warmth of Tom Harris, Jon Rotheram and Tom Hurst’s menu is outstanding. This is British comfort food elevated to the theatrical – rich, brown crab soup, crispy sourdough splattered with chive mayonnaise, deep red slices of cured beef and mustardy celeriac. For the main event, we feasted on a gigantic chicken, leek and girolle pie – presented like a Brutalist prop with two crudely crossed silver spoons and served with hand-cut chips and lettuce drenched in tarragon and buttermilk dressing. Artful yet approachable, this is culinary design as an extension of the National’s ethos.

And the design itself furthers this connection, prioritising both past and future. Named after the National’s architect Denys Lasdun, the restaurant is a Brutalist masterpiece accessed through a futuristic porthole door – think mirror surfaces, silver sputnik lights, shining brass and starched white tablecloths. It is both a continuation of what lies outside and an elegantly snug cocoon from somewhere else entirely.

Our server, Tomas, was a Welsh actor – recently graduated from a London drama school and auditioning between shifts. Through the glass window, Holly and I watched people on the stairs clutching programmes, kissing cheeks, shaking off the rain and removing anoraks. Inside, people caught up over communal food – sharing stories and checking their watches. At 7.15 pm, bills were paid and excited punters moved into the next act of their evening. I actually missed the beginning of the show, to Tomas’ horror, content to watch the restaurant’s stage empty. The dimming of its own house lights.

It is precisely the rush and buzz of Lasdun’s great in-and-out food that makes this brutal, stark setting a place of momentum and occasion. And an occasion it has to be. Theatre is expensive now – so is food – and eating at 6 pm is no longer only for Americans. The Lasdun is great precisely because of the theatre scene it sits within.

Pre-theatre dining: six syllables reimagined.

National Theatre, Upper Ground

London, SE1 9PX

@lasdunrestaurant