Whisk the milk, sugar, corn syrup and salt together in a heavy-bottomed saucepan. Cook over medium-high heat, stirring occasionally, until mixture just comes to a simmer.

Reduce heat to medium-low and fiddle around with the heat until the mixture is just barely simmering - a few bubbles here and there. You want it just hot enough to release steam and reduce down the mixture, but not so hot that it turns into caramel.

When the color of the mixture starts to deepen a little, keep a close eye on it. Once it starts developing that light caramel color, it cooks fast and thickens quickly. Pull it off the stove as soon as it is just a little thinner than store-bought sweetened condensed milk (about the consistency of pancake syrup). It will thicken slightly as it cools.

Cool for 15 minutes and pour in a clean, sterilized jar. Cover and rest until completely cool. Refrigerate and use within 2 weeks. Makes about 1 1/4 cups or 10 fluid ounces, which is the equivalent of a 14 ounce can (which is measured by weight).