Step 1Fill a large bowl with ice water and set a smaller bowl inside. Set a fine-mesh strainer in the smaller bowl. In a medium bowl, whisk together the egg yolks and cornstarch.
Step 2Combine the milk, sugar, milk powder, corn syrup and salt in a 4-quart saucepan and whisk to break up and dissolve the milk powder. Heat the milk mixture over high heat until it begins to bubble, then immediately remove from the heat.
Step 3Slowly add one-half cup of the hot milk mixture to the bowl with the eggs, whisking constantly. Continue to whisk in half of the milk, one-half cup at a time, enough to warm the eggs slightly.
Step 4Pour the egg and milk mixture into the pot with the milk, return the pot to medium-low heat and cook, stirring constantly with the whisk or a wooden spoon, until the gelato base thickens enough to coat the back of a spoon.
Step 5Pour the gelato base through the strainer into the bowl set over ice water and set aside to cool to room temperature. Transfer the base to an airtight container and refrigerate for at least several hours and up to three days.
Step 6Remove the ice cream mixture from the refrigerator, pour it into a bowl and stir in the cream and olive oil. Pour the mixture into the bowl of an ice cream or gelato maker, and spin it according to the machine instructions. Serve the gelato straight from the maker or transfer it to an airtight container and place it in the freezer until you're ready to serve it. Serve the gelato within a few hours of spinning it, before it hardens.