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1
Combine 1/2 cup plus 2 tablespoons sugar and the water in a heavy saucepan.
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2
Heat over medium, stirring occasionally, until sugar is dissolved and syrup is clear.
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3
Stop stirring, and cook until syrup comes to a boil, washing down sides of pan with a wet pastry brush to prevent crystals from forming.
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4
Continue to boil, gently swirling pan occasionally to color evenly, until mixture is very dark amber.
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5
Remove from heat; add cream in a steady stream (the mixture will spatter), stirring with a wooden spoon until smooth and combined.
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6
Let cool.
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7
With an electric mixer on medium-high speed, cream butter until pale and fluffy.
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8
In the heatproof bowl of a standing electric mixer, combine remaining 1/2 cup sugar and the egg whites.
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9
Set bowl over a pan of simmering water; whisk constantly by hand until mixture is warm to the touch and sugar has dissolved (the mixture should feel completely smooth when rubbed between your fingertips).
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10
Attach bowl to the mixer fitted with the whisk attachment.
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11
Starting on low and gradually increasing to medium-high speed, mix until stiff (but not dry) peaks form.
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12
Continue whisking until egg mixture is fluffy and glossy, and completely cool (test by touching the bottom of the bowl), about 10 minutes.
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13
Reduce speed to medium-low.
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14
Add beaten butter, about 1/4 cup at a time, mixing well after each addition.
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15
Mix in vanilla.
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16
Switch to the paddle attachment.
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17
With mixer on medium-low speed, very slowly pour in caramel; beat 5 minutes.
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18
Scrape down sides of bowl, and continue to beat until caramel is fully incorporated.
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19
Keep buttercream at room temperature if using the same day, or transfer to an airtight container and refrigerate up to 3 days or freeze up to 1 month.
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20
Before using, bring to room temperature and beat with paddle attachment on low speed until smooth again, about 5 minutes.
