Buckle makes use of underripe blackberries

Fresh blackberries, when perfectly ripe, stand alone as the perfect mouthful of pure fruit. Unfortunately, though, too often the less-than-ripe specimens get mixed in with the ready ones.

The blackberry's ripening pattern takes it from green to red to that telltale shade of deep purplish blue, which is the indicator of ripeness. A blackberry is only truly sweet and ripe if 100 percent of the drupelets have reached that saturated dark hue. If even a single drupelet is still red, chances are the entire berry will be sour.

What to do if your precious haul is an uneven combination or ripe and unripe• Make a buckle.

"A what?" you might inquire.

A buckle is a yellow cake with a generous amount of berries folded directly into the batter. This is a wonderful way to make good use of less-than-optimally sweet blackberries. This one tastes best when served warm, with a premium vanilla yogurt -- regular or frozen -- on the side, for a delightful afternoon tea or weekend brunch.

In the off-season (or the not-yet-season) you can make this with frozen, unsweetened blackberries, which are pretty easy to find, bagged, in the freezers of most grocery stores. Don't bother to defrost them -- just break them up so that they are separate, and proceed.

Raspberries make a good substitute if you can't get blackberries.

Unwrap the butter well ahead of time, and let it soften directly in the mixing bowl.

• Nonstick vegetable cooking spray, for coating pan

• 3 cups blackberries, fresh or frozen unsweetened

• 2/3 cup granulated sugar, plus 1 tablespoon for sweetening berries

• 3/4 cup (1 1/2 sticks) unsalted butter, softened

• 1 1/2 teaspoons pure vanilla extract

• 3 large eggs

• 1 cup unbleached all-purpose flour

• 1/2 teaspoon baking powder

• 1/4 teaspoon salt (rounded measure)

• 1 1/2 teaspoons minced or grated lemon zest

• Vanilla yogurt (frozen or regular), optional

Heat the oven to 350 degrees. Lightly coat an 8-inch-square pan or its equivalent with nonstick vegetable cooking spray.

Place the blackberries in a bowl and toss gently with 1 tablespoon sugar (or more, if they are very tart or underripe). Set aside.

In a medium-size mixing bowl, cream the butter with 2/3 cup sugar until light and fluffy. Add the vanilla and the eggs one at a time, beating well after each.

In a separate bowl, stir together the flour, baking powder, salt and lemon zest. Stir this into the butter mixture until well combined, and fold in the berries at the end.

Turn the batter into the prepared pan. Bake for 45 minutes to an hour, or until the top is uniformly golden and springy to the touch. Cool on a rack for at least 15 minutes before serving. Serve with vanilla yogurt, if desired.

Makes 6 or more servings.