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1
Prepare an ice bath; set aside.
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2
In a small bowl, combine the espresso powder and hot water, and stir until dissolved; set aside.
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3
In a medium bowl, combine the whole eggs, egg yolks, and 1 cup sugar.
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4
Whisk to combine.
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5
In a medium saucepan, combine the milk, vanilla seeds, cornstarch, salt, and remaining cup of sugar.
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6
Bring to a boil over medium-high heat, whisking constantly.
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7
Remove from the heat; slowly pour about a third of the hot milk mixture into the egg mixture, whisking constantly until combined.
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8
Pour egg mixture back into the remaining milk, whisking constantly.
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9
Return saucepan to medium-high heat.
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10
Bring to a boil, whisking constantly, until mixture is thick enough to hold a trail when you drag a wooden spoon through it, about 3 minutes.
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11
Whisk in butter, one piece at a time.
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12
Whisk in chopped chocolate and espresso mixture; continue whisking until smooth and combined.
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13
Strain the mixture into a large, heatproof bowl.
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14
Cover with plastic wrap, pressing it directly onto the surface to prevent a skin from forming.
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15
Place in the ice bath until completely chilled, stirring occasionally, about 30 minutes.
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16
Cover and refrigerate until ready to use, up to 3 days.
