BERKELEY, Calif. - Classic cake-making calls for eggs, flour, butter and sugar. But some bakers are juicing up the flavor by throwing liquor into the mix.

Or, as Terry Lee Stone, co-author of the recently published "Booze Cakes" cookbook puts it, "Baking is fun and drinking is fun - let's combine them!"

Stone and Krystina Castella, friends from teaching at a design college in Pasadena, started working on the book after Stone was inspired when making an old cake recipe of her mother's that called for adding alcohol.

But the concoctions they came up with for their book go well beyond the typically tame "add a tablespoon of kirsch" school of cooking with liquor.

"It was really important to us that you tasted the alcohol," Castella says. "When we first developed the idea, there really wasn't much out there. We found people adding different liquors and alcohols to food, but not much in baking."

The recipes they did find generally used liquor as a substitute for vanilla. "So we would find (recipes calling for) one teaspoon of rum. One teaspoon of rum is not going to really give it a rum flavor. You might need 1/4 cup of rum and then soak it in rum and having rum frosting."

Castella and Stone have invited readers to explore variations on their themes and bloggers have enthusiastically taken to it, posting their results on the "Booze Cakes" Facebook page.

In fact, there seems to be a surge of interest in baking with libations. A second book, "The Boozy Baker," by the aptly named Lucy Baker, also was released this year.

Baker sees a general trend toward slow-paced activities like baking that she views as a reaction to a high-speed, 24-7 world. "People are looking for ways to relax, to kick back, to reconnect. Having a speakeasy inspired cocktail is one way to do that and another way to do that is baking."

Baker was inspired to try adding liquor while looking for something to do with a bottle of ouzo that ended up in her pantry. The anise-flavored drink worked surprisingly well in a cake, and soon she was "pouring in a little bit of this and a little bit of that into all my different recipes and finding that it really worked well." The alcohol enhanced the flavor and made dessert "seem a little more indulgent."

Her book covers pies, cookies and other desserts as well as cakes, and recipes include a margarita meringue pie and Champagne layer cake. Among her discoveries, ginger liqueur goes great with peach and Port is surprisingly good with fruit.

In their book, Castella and Stone tackle a little chemistry along with confectionery, providing a chart on how much alcohol is likely to remain in cakes depending on how large they are and how long they bake. Some of the alcohol burns off, but not all. And whatever you use for soaking or put in frosting, stays there.

They cook with spirits, wine and beer and went for some unusual combinations, such as their Jagermeister Deutsch German chocolate cake.

They have a chapter on the classics, such as fruit cakes and Black Forest cherry cake, as well as new twists, such as a cocktail cupcake chapter that incorporates the flavors of classic drinks.

As they explored alcohol as a flavoring, they found some spirits work better than others.

Castella, who isn't fond of gin in drinks, didn't like it in cakes either. "I felt like it was too antiseptic tasting."

But bourbon turned out to be a winner, as did the combination of tequila and chocolate.

Cooking with liquor is something that French pastry chefs have done for years, notes cookbook author Dorie Greenspan, whose latest is "Around My French Table." Those chefs "always had a little liquor cabinet, often under lock and key, used for flavoring," she said.

What seems to be new about the approach is marrying the trend of culinary cocktails, in which liquors are being used in new and creative ways, with baking. "This is a rebirth and a rethinking," she said.