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1
Preheat oven to 425F.
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2
Unfold pastry sheet, then turn over (to prevent creases from splitting during baking).
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3
Cut 6 (4 1/2-inch) triangles from sheet with a long sharp knife and a ruler.
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4
Arrange triangles on a greased baking sheet and lightly prick centers a few times with a fork.
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5
Bake in middle of oven until puffed and golden brown, 15 to 18 minutes.
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6
Transfer to a rack and cool.
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7
Stir together cornstarch, water, and lemon juice in a small saucepan.
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8
Add berries and sugar and simmer over moderately high heat, stirring and breaking up berries, until thickened, 3 to 4 minutes.
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9
Force puree through a fine sieve into a bowl, pressing hard on solids, then cool puree at room temperature.
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10
Boil wine in another small saucepan until reduced to about 1 tablespoon, 10 to 12 minutes, then cool.
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11
Beat cream with confectioners sugar and zest in a bowl until it just holds stiff peaks.
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12
Fold wine into cream until just incorporated, then chill.
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13
Split each pastry triangle in half horizontally and make a sandwich with about 1 1/2 tablespoons cream.
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14
Spread 1 teaspoon puree on top of each pastry, leaving a 1/4-inch border (there will be puree left over).
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15
Decoratively arrange some raspberries and blackberries on top and sift some confectioners sugar over berries.
