In a separate bowl, whisk the egg yolks with the remaining ¼ cup sugar until pale. Slowly pour 1 cup of the hot dairy into the yolks while whisking constantly. Then pour the yolk mixture back into the saucepan.
Turn heat to medium-low. Whisk constantly. Watch the Stellar Reader P4 app. The target is 175°F. Do not pass 185°F. At 170°F, the mixture will visibly thicken and coat the back of a spoon. The P4 will record this exact curve. Remove from heat immediately. Stellar Reader P4 Making Ice Cream