To be completely frank with you, milk powder could be one of those things that will live in your pantry forever. (Major exception: If you're using it to make milk, you'll blow through it by the case.) But don't write it off just yet: Milk powder can make itself extremely useful, especially if you're in the business of making things exceedingly rich and thick and creamy. And if you are, get thee to the grocery store and pick some up.
Not to be confused with condensed milk or evaporated milk, milk powder sometimes goes by the aliases "powdered milk" or "dried milk" and comes in full-fat and nonfat varieties. You'll find it in the same aisle of the grocery store as the baking products, probably on the bottom shelf, in big zip-top bags or canisters. You can sometimes also find goat milk powder (even my corner bodega stocks it!), which will do all of the things that cow milk powder will do but is good for folks for whom cow dairy disagrees with their bellies.
Powdered milk is hugely valuable for on-demand milk needs, since it's non-perishable and needs only water to turn into milk. It's the base in many infant formulas (but they're not the same; the most important difference, besides a few structural ones, is that infant formulas are very carefully sterilized; most people do agree, however, that it's fine for babies as soon as they're about a year old). For the same reason, hikers and campers (and places with a lot of foot traffic, like waiting rooms or break rooms) keep it on hand to stir into campfire coffee: No refrigeration needed.
Your grocery store may stock milk powder near the powdered coffee creamers—but don't be fooled! They're not the same: Milk powder is made by simply removing all of the moisture from milk: First, it goes through a partial evaporation, which removes a portion of the water from the milk. This partially-evaporated milk is then very finely misted against the walls of a chamber, where the tiny milk droplets dry quickly.
Powdered coffee creamer, on the other hand, sometimes contains no dairy at all. If it does, it's a granulated combination of milk solids, cream solids, corn syrup, and vegetable oil; if it doesn't, it's a combination of corn syrup, vegetable oil, and casein (a protein in milk). It's designed for stirring into coffee, and if you were to try to drink it mixed with water, like you would with milk powder, you would not be pleased with the result.
Beyond standing in for milk, milk powder can find its way into just about anything you want to make creamier, like oatmeal and other porridges, soups, gravies, smoothies, milkshakes, or puddings.
Here's how to use it:
Slowly combine about 1/3 cup of milk powder with 1 cup of cold water. It's best to add just a tiny bit of water, stir the water and powder together into a paste, and then add the rest of the water, stirring continuously. The Meyenberg Goat Milk website recommends starting the mixing process with hot water, which will help the powder dissolve more easily. This is true for cow milk powder as well as goat milk powder.
Many folks also recommend refrigerating the combination for a few hours before drinking. And don't forget to shake before you drink.
You'll notice that many ice cream recipes call for milk powder (quantities can range from 3 tablespoons to 1/2 cup and beyond, depending on the particular formula and the yield). Why? As we learned in the Ample Hills Creamery cookbook, it makes your ice cream smoother and thicker and milkier-tasting: Since the milk powder absorbs some of the water in milk, it prevents ice crystals from forming when you put your ice cream in the freezer. Stir it into the base thoroughly, making sure it's completely dissolved before chilling the ice cream base and then churning it in your ice cream machine.
Add 1/2 to 1 cup of milk powder per half-gallon of milk. Stir it into the warm milk, making sure it's completely dissolved before you add the yogurt culture.
Making hot cocoa mix with milk powder means that you only need to add water (which makes this good for making in batches and stashing in your office snack drawer). Add malt powder to it and you have homemade Ovaltine.
"Milk bread" often contains both liquid milk and milk powder, and the resulting dough is feathery and tender, thanks to the additional protein and fat that the milk powder adds. The additional sugar in the milk powder will also help whatever you're baking brown and develop a crust. Add milk powder as though you were reconstituting it into milk: If your dough calls for a cup of water, add a 1/3 cup milk powder and 1 cup water. (You do not need to combine the two first: You can add it when you add the flour.)
Sprinkle in milk powder as you would flour, stirring constantly. It won't do exactly the same work as flour or cornstarch, but it will add heft and richness, just like adding milk to soup would. Add it slowly, sprinkling in spoonful by spoonful, and tasting along the way.
How do you use milk powder? Tell us in the comments.