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1
Combine sugar and cornstarch in heavy medium saucepan.
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2
Whisk in 1 1/4 cups buttermilk and lemon juice.
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3
Whisk in egg yolk.
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4
Simmer mixture over medium heat until thick, stirring constantly, about 1 minute.
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5
Stir in butter, lemon peel and food coloring.
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6
Remove from heat.
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7
Transfer to medium bowl.
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8
Whisk in 2 tablespoons buttermilk.
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9
cover surface of filling with plastic wrap; cool to room temperature.
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10
(Can be made 1 day ahead.
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11
Chill.)
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12
Preheat oven to 375F.
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13
Spray 13 1/4 x 9 1/4 x 3/8-inch jelly roll pan with vegetable oil spray.
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14
Line pan with waxed paper and spray paper.
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15
Lightly coat paper with flour; tap out excess.
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16
Combine flour and baking powder in medium bowl.
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17
combine eggs and egg whites in large metal bowl.
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18
Set bowl over saucepan of simmering water (do not allow bowl to touch water).
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19
Whisk eggs until just warm to touch, about 2 minutes.
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20
Remove bowl from over water.
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21
Add sugar and salt.
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22
Using electric mixer, beat egg mixture until fluffy, thick and pale, about 6 minutes.
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23
Sift flour mixture atop egg mixture; gently fold in.
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24
Fold in butter (do not overmix or batter will deflate).
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25
Transfer batter to prepared pan.
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26
Tilt pan to coat thinly.
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27
Bake until top springs back when touched and edges are light golden, about 12 minutes.
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28
Sift powdered sugar over hot cake.
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29
Place 2 paper towels over cake.
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30
Place rimless baking sheet atop cake and invert cake onto baking sheet.
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31
Remove waxed paper.
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32
Trim edges of cake to form 13 x 8-inch rectangle.
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33
Starting at 1 short end of cake, roll up jelly roll style, discarding paper towels.
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34
Cool completely.
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35
Unroll cake.
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36
Whisk filling to smooth.
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37
Spread filling evenly over surface of cake.
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38
Starting at 1 short end of cake re-roll cake jelly roll style.
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39
Transfer cake, seam side down to platter.
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40
Cover with plastic wrap and refrigerate 2 hours.
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41
(Can be prepared 1 day ahead.
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42
Keep chilled.)
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43
Cut cake into eight 1-inch slices.
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44
Garnish with lemon slices and mint sprigs, if desired.
