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1
Sift together flour, cocoa, and salt into a bowl.
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2
Melt chocolate in a heatproof bowl set over a pan of simmering water, stirring until smooth; set aside to cool.
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3
Put butter and 1/4 cup granulated sugar into the bowl of a mixer fitted with the paddle attachment; mix on medium speed until pale and fluffy.
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4
Mix in yolk, vanilla, and chocolate.
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5
Reduce speed to low.
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6
Mix in flour mixture until just combined.
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7
Refrigerate, covered, 1 hour.
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8
Preheat oven to 350F.
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9
Put 6 teaspoons granulated sugar into a small bowl.
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10
Form dough into 3/4-inch balls; roll in sugar to coat.
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11
Space 1 inch apart on baking sheets lined with parchment.
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12
Press center of each ball with your thumb.
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13
Bake 10 minutes.
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14
Press centers again with end of a wooden spoon, making 3/4-inch indentations.
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15
Bake until slightly cracked and set, about 5 minutes more.
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16
Cool completely on racks.
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17
(Unfilled cookies can be stored in airtight containers at room temperature up to 3 days.)
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18
Stir cream cheese and confectioners sugar in a bowl.
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19
Toss berries with remaining 1/2 teaspoon granulated sugar in another bowl.
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20
Spoon cream cheese mixture into centers of cookies; top with berries, dividing evenly.
