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1
Combine first 4 ingredients in bowl.
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2
Add flour and stir just until blended; let stand 5 minutes.
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3
Press dough onto bottom and up sides of 9- to 91/2-inch-diameter tart pan with removable bottom.
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4
Chill 30 minutes.
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5
Position rack in bottom third of oven and preheat to 350F.
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6
Bake crust until deep golden, pressing down with back of spoon if bubbles form, about 25 minutes.
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7
Cool crust in pan on rack.
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8
Combine chocolate, butter, and both peels in medium metal bowl.
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9
Place bowl in skillet of barely simmering water set over low heat.
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10
Stir just until chocolate and butter are melted and smooth.
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11
Remove bowl from water.
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12
Place fine strainer over bowl with melted chocolate.
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13
Keep skillet with water set over low heat.
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14
Whisk egg yolk in small metal bowl to blend.
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15
Gradually whisk in 1/4 cup boiling water.
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16
Place bowl in skillet of hot water; stir constantly with heatproof rubber spatula, scraping bottom of bowl to prevent egg from cooking, until instant-read thermometer inserted into egg mixture registers 160F, about 3 minutes.
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17
Immediately pour egg mixture into strainer set over bowl of chocolate.
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18
Stir just until egg is incorporated into chocolate and mixture is smooth.
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19
Pour chocolate filling into crust; tilt slightly to spread evenly (crust will not be completely filled).
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20
Cover and chill overnight or up to 2 days.
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21
Before serving, let tart soften slightly at room temperature.
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22
Remove pan sides.
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23
Place tart on platter.
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24
Using pastry bag fitted with star tip, pipe whipped cream rosettes around edge of tart.
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25
Garnish with candied peel.
