From my own long running quest to find an authentic gelato recipe that works. I am shooting for a great vanilla gelato base that I can drizzle melted chocolate into for a real-deal stracciatella (chocolate chip gelato).
Making a few slight changes from previous attempts, I ended up with a wonderfully creamy, near perfect quart of gelato. Here's how:
I simmered 3 cups of whole milk in a small saucepan with a vanilla bean. I pulled the vanilla bean out of a batch of homemade vanilla extract that has been brewing for well over a year. The bean was nice and supple with lots of little vanilla bean flecks waiting to be squeezed out into the pot of milk.
In a large glass measuring cup I poured one more cup of milk, and then added 1 cup of sugar, and 3 tablespoons + 2 teaspoons of corn starch, and mixed that all up. My last attempt, I used 3 tablespoons of cornstarch, and I don't think the mixture thickened up enough.
As my milk started to simmer, I took it off the heat, and poured the cornstarch mix into the saucepan with the milk and vanilla bean (stirring the whole time). Placed it back on the low-med heat, and stirred, and stirred, and stirred, until things thickened up, about 10-12 minutes. It ended up being thicker than, say, a runny milkshake---but thinner than a super frosty one.
I poured it though a strainer into a mixing bowl, let it cool off on the counter for 20 minutes or so, and then into the fridge for a couple hours, until it was completely chilled. Don't skimp here, this is another place I've run into trouble in the past.
Also, take care that your ice-cream maker itself is well prepped. Make sure it has been in the freezer for as long as possible, at least over night.
For the chocolate 'chips'....I threw a few chunks of bittersweet chocolate into a small saucepan over low heat---just until the chocolate starts to melt. Kept stirring it. Turned off the heat, and let it cool a bit. I then drizzled it into the churning ice-cream maker after the gelato really started to thicken up. Do it right, and you'll get nice chunks of chocolate all throughout your gelato.