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1
Make the filling: Bring the milk to a simmer in a medium saucepan over medium heat.
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2
Whisk the sugar, cornstarch, vanilla and egg in a medium heatproof bowl until smooth.
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3
Gradually whisk half of the hot milk into the sugar mixture, then return to the pan with the remaining milk.
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4
Reduce the heat to medium low and cook, whisking constantly, until the mixture boils and thickens, 2 to 3 minutes.
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5
Transfer to a bowl (strain through a fine-mesh sieve if it looks lumpy), then stir in the chocolate until melted.
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6
Press plastic wrap directly onto the surface and refrigerate until cold, at least 1 hour.
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7
Meanwhile, make the ganache: Put the chocolate and salt in a large heatproof bowl.
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8
Bring 1 1/2 cups heavy cream to a simmer in a saucepan over medium heat; pour over the chocolate and let sit 5 minutes, then whisk until smooth.
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9
Pour 3/4 cup of the ganache into a liquid measuring cup and set aside at room temperature.
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10
Refrigerate the remaining ganache in the bowl until thick but not set, about 1 hour.
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11
Assemble the cake: Put 1 cake layer on a platter; spread the filling on top, stopping about 1/2 inch from the edge.
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12
Top with the second cake layer and press down gently.
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13
Add the remaining 2 tablespoons heavy cream to the chilled ganache and beat with a mixer on medium speed until just fluffy, about 1 minute (do not overbeat).
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14
Frost the whole cake with the whipped ganache.
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15
Pour the room-temperature ganache on top, letting it drip down the sides.
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16
Let set before slicing, about 30 minutes.
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17
Photograph by Levi Brown
