MICHELLE LOCKE, For The Associated Press

Smooth, sweet, cold and just the ticket for contracting a case of brain freeze on a sweltering summer day. There's a reason milkshakes are a staple of American childhood.

But why should the kids have all the fun?

Sure, strawberry, chocolate and vanilla make fine beverages for summer. But for an after-dinner twist just for the grownups, how about stirring in a little black raspberry liqueur or a dash of bourbon? Bartenders around the country are doing just that as they shake up the seasonal staple.

At Hill Country Barbecue Market in Washington, the maple bourbon milkshake pays homage to the retro diners and soda fountains of the 1950s. Served in the classic style with two straws in one large glass, this shake made for sharing combines a rich blend of bourbon with vanilla ice cream and maple syrup infused with vanilla beans. The whole thing is topped with maraschino cherries in the classic tradition.

In Seattle, chef Walter Pisano of Tulio Ristorante has a "desserts for grown-ups" menu that includes a prosecco float made of honey gelato, honey-infused whipped cream and prosecco.

And how about revisiting that old favorite, the root beer float? At Harry Denton's Starlight Room in San Francisco, bar manager Joel Teitelbaum serves a hard root beer float that includes Zaya aged rum with vanilla notes and Averna, an Italian bitter that adds a chocolate note.

Also in San Francisco, pastry chef Francis Ang at Fifth Floor restaurant has a wild take on the shake.

He serves a foie gras milkshake featuring foie gras ice cream and walnut liquor. (This treat won't last much longer than ice cream left out in the sun since California is banning force-feeding water fowl to create foie gras effective July.) The ice cream is mixed with milk, sugar, a little salt and the walnut liquor, then poured over ice and topped with root beer.

Want to try this at home? Here are a couple of recipes to let you shake up your own summer indulgence.

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PURPLE VELVET MILKSHAKE

Purely for adults, this silky smooth milkshake is perfect for an after dinner treat. The deep, rich flavors of black raspberry ice cream combine with the barrel-aged smokiness of bourbon to make a dark, silky indulgence.

Start to finish: 10 minutes

Servings: 2

1 cup black raspberry ice cream

1/2 cup vanilla ice cream

2 ounces bourbon

1 ounce Chambord liqueur

Fresh blackberries

Fresh mint leaves

In a blender, combine both ice creams, the bourbon and Chambord, then blend until smooth. Divide between 2 glasses, then garnish each with fresh blackberries and mint leaves.

Nutrition information per serving (values are rounded to the nearest whole number): 290 calories; 80 calories from fat (28 percent of total calories); 9 g fat (6 g saturated; 0 g trans fats); 35 mg cholesterol; 31 g carbohydrate; 3 g protein; 1 g fiber; 65 mg sodium.

(Recipe by Alison Ladman)

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TOASTED MALT MILKSHAKE

This milkshake combines the creamy richness of the classic malted milkshake with the flavor of a toasted almond cocktail. The result is a toasty, malty, frothy treat. Malted milk powder can be found in the grocer's baking aisle, or sometimes with the coffee and tea.

Start to finish: 10 minutes

Servings: 2

1/4 cup Ovaltine Classic Malt

1 cup vanilla ice cream

1 ounce amaretto liqueur

1 ounce Kahlua liqueur

1 ounce Frangelico liqueur

Finely chopped toasted almonds, to garnish

In a blender, combine the malted milk powder, vanilla ice cream, amaretto, Kahlua and Frangelico. Blend until smooth. Slightly moisten the rims of 2 glasses, then overturn them and dip the rims in the toasted almonds. Pour the milkshake into the center of the glasses without disturbing the rims.

Nutrition information per serving (values are rounded to the nearest whole number): 370 calories; 70 calories from fat 19 percent of total calories); 8 g fat (4.5 g saturated; 0 g trans fats); 30 mg cholesterol; 53 g carbohydrate; 5 g protein; 1 g fiber; 130 mg sodium.

(Recipe by Alison Ladman)