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Preheat the oven
to 400°F/200°C/gas 6. Butter a cookie sheet. Use a pencil and ruler to draw a 12 x 8-inch (30 x
20-cm) rectangle on a sheet of parchment paper.
-
Draw
triangles, points facing inward, at each end of the
rectangle to resemble a double-edged bowtie. Cut out
the template.
-
Place the template on prepared cookie
sheet. Beat the butter and confectioners' sugar in
a large bowl with an electric mixer at high speed
until creamy.
-
Stir in the egg whites, followed by
the flour and salt. If the mixture separates,
place over barely simmering water and mix.
-
Set
aside 2 tablespoons of the mixture. Stir the cocoa
into the remaining batter.
-
Use a thin metal
spatula to spread a small amount of plain cookie
batter around the inside edge of the template to
form a border.
-
Spread the remaining plain batter
in the center of the template. Spoon the cocoa
batter into a small plastic freezer bag. Cut off the
corner and pipe over the edges.
-
Bake for 8-10
minutes, or until just golden. Use a spatula to
loosen the edges and transfer to a rack to cool
completely.