Seconds.

That’s how long the new soft-serve ice cream machine had been up and running last summer at popular South End bakery Blackbird Doughnuts before an enterprising employee took stock of the situation and — in a stroke of culinary genius — suggested, “Why don’t we just make ice cream doughnuts?’’

Thus, Blackbird’s ice cream sandwich doughnut ($6) was born — a summertime indulgence every bit as glorious as it sounds.

Patrons simply pick one of the shop’s dozen or so from-scratch artisanal doughnuts — except for the filled ones — and the shop will halve it, plop a dollop of vanilla, chocolate, or swirl soft-serve upon it, and hand it over. The shop’s been selling somewhere in the neighborhood of 25-30 a day this summer, and Anna Roine Perna, Blackbird’s head baker, recommends the chocolate old-fashioned doughnut with chocolate ice cream, the salted toffee doughnut with swirl, and the funfetti doughnut with vanilla.

The good news? Blackbird is happy to add garnishes like sprinkles, or heat the doughnut to create a melty mess of flavor.

The better news? The sandwiches aren’t going anywhere, as the shop plans to keep hawking the item even after summer’s dog days have passed.

“We want to keep doing it,’’ Roine Perna says, “as long as people want to keep eating doughnuts and ice cream.’’ 492 Tremont St., South End, Boston, 617-482-9000, www.blackbirddoughnuts.com

DUGAN ARNETT

Dugan Arnett can be reached at dugan.arnett@globe.com.