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1
Whisk together confectioners sugar, flour, and salt in a large bowl; make a well in the center.
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2
Add butter, egg whites, cream, and vanilla.
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3
Stir until well combined.
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4
Refrigerate, covered, at least 2 hours or up to overnight.
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5
Preheat oven to 425F.
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6
Line two baking sheets with nonstick baking mats (such as Silpats).
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7
Make four cookies at once: Spoon a heaping tablespoon of batter onto baking sheet.
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8
Using an offset spatula, spread batter into a very thin 6 by 3 1/2-inch oval.
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9
Repeat, making two more ovals of batter on the sheet.
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10
Bake just until brown around edges, about 6 minutes.
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11
When cookies come out of the oven, use a long offset spatula to quickly transfer cookies, one at a time, to a work surface; roll around a chopstick or a thin wooden dowel, forming a cylinder shape; transfer to a wire rack, and let cool completely.
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12
Repeat to roll remaining three cookies.
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13
If they harden too quickly, return baking sheet to oven for 30 seconds.
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14
Repeat with remaining batter.
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15
Put chocolate into a heatproof bowl set over a pan of simmering water; stir often until smooth.
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16
Stir in oil.
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17
Let cool slightly.
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18
Dip about 2 inches of each cooled cookie into chocolate.
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19
Roll dipped edge in chopped nuts, if desired.
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20
Transfer to a wire rack, placing dipped section off the edge, to set.
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21
Cookies can be stored between layers of waxed paper in an airtight container at room temperature up to 3 days.