Spread walnuts in one layer in a moderate oven and stir as they toast. Pull them when they smell nutty and look slightly darker, then transfer them to a cool plate to stop the hot tray from browning them further.
Start with a small tray
Preheat the oven to 325 degrees Fahrenheit, about 165 Celsius. Spread half a cup of walnut halves in a single layer on a rimmed sheet. Break up any piles so each piece has room around it. Put the tray near the center of the oven and set a timer for five minutes as a reminder to check and stir.
Judge the pieces as well as the clock
Move the outside pieces toward the center and separate pieces that stick together. Check again as color and aroma develop. Ten to fifteen minutes is a reference range from King Arthur Baking. A small batch or small pieces can be ready sooner, so use what you see and smell. Transfer the nuts with a spatula to a heat-safe plate and let them cool before chopping. If the nuts will bake again on top of a dish, start with a lighter toast.
Compare two batches
Toast halves first, then try a separate batch of chopped walnuts. Record the first time you notice a toasted smell for each batch. Which size calls for an earlier check in your oven?
