Heat 1 1/2 cups of heavy cream and the half-and-half in a 2 1/2-qt saucepan over medium-high heat. Bring to a boil. While the cream is heating, combine the egg yolks, eggs, sugar, cornstarch, and instant espresso powder in the bowl of an electric mixer fitted with a paddle. Beat the mixture on high for 2 minutes, scrape down the sides of the bowl, and continue mixing on high until the mixture is slightly thickened, about 1 1/2 to 2 minutes. (At this point the cream should be boiling. If not, adjust the mixer speed to low and continue to mix until the cream boils. If his is not done, the eggs will develop undesirable lumps.) Pour the boiling cream into the beaten egg mixture and whisk to combine. Return to the saucepan and heat over medium-high heat, whisking constantly, until the cream reaches a temperature of 180 degrees, about 5 to 6 minutes. Remove from the heat and transfer to a stainless steel bowl. Cool the espresso-custard mixture in an ice-water bath to a temperature for 40 to 45 degrees, about 20 to 25 minutes. - KAREN PHILLIPS