Write-Up in The Boston Globe

PORTLAND, Maine — “I’ll give you $100 if you can find me two more doughnuts,” an older gentleman calls out as he and his wife march past the A-frame sidewalk sign reading “sold out,” and into The Holy Donut. The sign had already been out for an hour. Owner Leigh Kellis sighs, “I feel so bad when we run out.”

This is a typical Saturday morning for the 5-month-old shop in Portland’s Deering Oaks neighborhood, even though Kellis and her staff, several of whom are family members (she co-owns the business with her father, Allen), have continuously ramped up production since they opened. Nowadays, they turn out roughly 1,200 doughnuts a day in at least a dozen different flavors: plain wide rings dredged with cinnamon-sugar or dripping with maple, lemon, vanilla, or “mojito” lime glaze; sweet potato doughnuts laced with ginger; best-selling dark-chocolate doughnuts flecked with coarse sea salt. All doughnuts are $1.50 each, $8 per half-dozen, and $15 per dozen. To satisfy savory cravings, Kellis dreamed up a Hot Pocket-style fritter stuffed with bacon and sharp cheddar.

But even her plainer flavors are anything but ordinary. These remarkably light cake-style doughnuts contain no yeast, but both baking powder and baking soda. And they’re full of mashed potatoes. Kellis supplements the flour in the batter with spuds both as a tribute to Maine’s potato doughnut tradition — potatoes are the state’s biggest crop, and a more common ingredient in northern Maine doughnut recipes — and because potatoes make an especially airy, tender crumb.

Kellis had never made a doughnut until a couple years ago, when she was talking doughnuts with a friend and realized that her longtime love of the fried treats had turned into more than just a craving. She wanted it to be a career. “The next day, I went to a bookstore to write down recipes,” Kellis says. “I practiced making doughnuts every day at home.”

She stumbled on the potato recipe. She was frying her way through dozens of experiments when a potato-based batter from “The Joy of Cooking” grabbed her attention. Over the next five months, she tweaked the recipe, boiling, ricing, and incorporating varying amounts of mashed spuds into her recipe and serving up test samples daily to neighbors until she had a specimen she thought was worth selling.

“I took some doughnuts to the Coffee By Design in my neighborhood and asked them to sell them,” Kellis says. “They said they would, and I was over the moon.”

Then things got busy. Kellis was already holding down a full-time bartending job at a local pizza restaurant. The doughnuts business happened in her free time. “I would bartend until midnight and wake up at 5 a.m. to make one dozen doughnuts,” she says. “Then other Coffee By Design shops caught on, and Whole Foods had heard of them, and soon there were 10 to 12 other shops that wanted them. I went from making one dozen a day to 100 dozen a week.”

That’s when her dad came on board and they signed a lease on the old Terroni’s Market building on Park Avenue. Three months of renovations later — including investing in an industrial fryer and a mixer — they opened up shop and have served a nonstop line of customers ever since. “We call it ‘panic mode,’ ” Kellis says. “There’s a line out the door and we can’t make [the doughnuts] fast enough.”

Near-instant success hasn’t swayed her work ethic. Other than buying pre-boiled potatoes, Kellis and her team still do everything by hand — from rolling and cutting every doughnut to squeezing fresh citrus juices for glazes. She’s also quick to acknowledge her staff, especially her father, mother, and sister. “I couldn’t be more grateful,” she says.

In the meantime, she’s starting to think forward. More flavors are in the works, including pumpkin and cider doughnuts. And once she finds a source for “mean homemade jam,” possibly jellies, too. “I’m a stickler for the best ingredients,” she says.

She’s also starting to think bigger.

“We would like a couple more stores in the Portland area,” Kellis says. “Every neighborhood should have a doughnut shop. It gets people so excited, like they’re kids. And it’s about personal growth — having an idea and watching it become something is beyond a dream.”

The Holy Donut, 194 Park Ave., Portland, Maine, 207-874-7774, www.theholydonutmaine.com.