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Some things are so much more than the sum of their parts. Take sweetened condensed milk. On the surface, it's simply fresh milk, cooked to remove about 60% of its water content and sweetened with enough sugar to form a heavy syrup. Yet, along the way, Maillard browning creates this beautiful complexity, giving it a toasty, toffee-like character.
Let's be clear—there's nothing wrong with the stuff in a can (though Max Falkowitz has proven that not all brands are created equal). But no brand can compare to made-from-scratch sweetened condensed milk, because when you're in charge of the dairy, sugar, and heat, truly magical things will happen, especially if you opt for the mellow sweetness of toasted sugar.
Controlling those variables gives homemade sweetened condensed milk more depth of flavor and body, while also allowing for customization, as ingredients like vanilla bean, cinnamon sticks, whole spices, and fresh herbs can be infused straight into the milk. Just take care to avoid acidic ingredients that can curdle the milk.
Now, I fully understand the convenience of canned dairy, but in a world where so many of us routinely binge entire seasons of television in one sitting, let's not pretend we don't have the time. A batch of homemade sweetened condensed milk takes 45 minutes from start to finish and requires no more effort than some idle stirring. By the time I finished up Game of Thrones, I could've amassed a lifetime supply. (Besides, multitasking varnishes my guilty pleasures in a sheen of productivity.)
The ingredients are simple: 32 ounces milk, seven ounces sugar, and six ounces heavy cream, plus a pinch of salt and whatever aromatics you choose. The cream adds a major dose of lactose for more flavorful browning, but more importantly, it prevents the milk from curdling as it cooks. Thanks to the fat content in the cream, it doesn't matter whether you use whole or skim milk, so feel free to grab whatever you have on hand.
Once it comes to a boil, the dairy will deepen from bright white to ivory as the lactose browns, which is why it's important to stir and scrape all the while with a flexible spatula. But so long as you've got some entertainment at hand (be it GoT or a magazine), the time will fly.
At the end of 45 minutes, it will be foamy and thick. (If not, feel free to turn up the heat; heavier gauges of cookware and weak burner outputs can slow things down.)
If you've got a digital scale, the recipe is even easier because you can use it to monitor the reduction—when the pot weighs 26 ounces less than when you started, it's done! That means 60% of the dairy's water content will have boiled away, reducing the mixture to exactly two cups or 19 ounces—further proof that a pint isn't a pound the world around.
Should you accidentally reduce the mixture too far, top it off with enough milk to reach two cups or 19 ounces, and hit the whole thing with an immersion blender to emulsify. (Of course, you'll need to first remove any added flavorings.) Transfer the sweetened condensed milk to a heat-safe jar. Mild aromatics, like vanilla, can be left in the jar to continue steeping, but remove spices and herbs to prevent the bitterness associated with over-extraction.
Cover and refrigerate until cool and thick, and store up to a month in the fridge. Generally speaking, you'll want to bring homemade sweetened condensed milk to room temperature before use; most recipes are based on "room-temperature" canned goods, and a massive drop in temperature can adversely thicken or curdle batters and doughs. Aside from the issue of temperature, the homemade version can be used interchangeably for store-bought.
My cookbook includes variations for incorporating ingredients like fresh ginger, dried lavender, whole spices for masala chai, herbs, and even goat's milk. I use sweetened condensed milk, whether plain or flavored, in everything from pumpkin pie and Key lime pie to marbled brownies and tres leches cake (plus a killer soft-serve, too). You can incorporate homemade sweetened condensed milk into your own favorite recipes as well, or use it as a simple sauce for other desserts and a sweetener for coffee or tea. That is, if you can refrain from just eating it with a spoon.