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1
Preheat oven to 400 F. Butter a 15- by 10 1/2-inch jelly-roll pan and line with wax paper or parchment paper.
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2
Butter and flour paper, knocking out excess flour.
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3
In a double boiler or a metal bowl set over a saucepan of barely simmering water melt chocolate, stirring until smooth, and remove double boiler or pan from heat.
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4
In a bowl with an electric mixer beat yolks, sugar, zest, and salt until thick, pale, and mixture forms a ribbon when beaters are lifted.
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5
Beat in melted chocolate until just combined.
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6
In another bowl with cleaned beaters beat whites until they just hold soft peaks.
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7
Stir one fourth whites into chocolate mixture to lighten and fold in remaining whites gently but thoroughly.
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8
Pour batter into jelly-roll pan, spreading evenly with a spatula, and bake in middle of oven 10 minutes, or until cake is springy to the touch.
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9
Cool cake in pan, covered with a dampened kitchen towel.
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10
With a sharp knife cut peel and pith from tangerines or oranges and cut sections free from membranes.
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11
In a bowl with an electric mixer beat cream with liqueur until it just holds stiff peaks and fold in fruit sections until just combined.
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12
Put a large sheet of foil (about 20 by 15 inches) on a work surface and lightly dust with cocoa powder.
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13
Invert cake onto foil and gently peel off paper.
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14
Spoon cream mixture evenly onto cake.
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15
Beginning with a short side and using foil as a guide, roll up roulade jelly-roll fashion and transfer to a platter, seam side down.
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16
Lightly dust roulade with cocoa powder.
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17
Roulade may be made 1 day ahead and chilled, loosely covered.
