Grappa Semifreddo with Espresso Sauce

Have ready a large bowl of ice and cold water.
Beat together yolks, sugar, and 1/3 cup grappa with an electric mixer in a metal bowl set over a saucepan of simmering water 10 minutes, or until thick and pale and mixture registers 170F on an instant-read thermometer.
Put bowl in ice bath and beat mixture until cold.
Beat whites with a pinch of salt in another bowl with cleaned beaters until they just hold stiff peaks.
Beat cream in a separate bowl until it holds soft peaks.
Whisk one third of whites into yolk mixture to lighten and fold in remaining whites and then cream, gently but thoroughly.
Spoon into molds and freeze, covered with plastic wrap, until firm, about 2 hours.
Cook sugar in a 2-quart heavy saucepan over moderately low heat, stirring slowly with a fork, until melted and pale golden.
Cook caramel without stirring, swirling pan, until deep golden.
Remove from heat.
Stir together boiling water, espresso powder, and lemon juice.
Carefully add to caramel (mixture will bubble up and vigorously steam), then cook over moderately low heat, stirring, until caramel is dissolved and sauce is smooth.
3Dip molds in hot water 5 seconds, then run a small thin knife around edges and invert onto plates.
Spoon a teaspoon of chilled grappa on top of each and drizzle plates with warm or room-temperature espresso sauce.