There are taste and texture benefits to using melted unsalted butter. Melting the fat creates a dense texture instead of a cakey texture. More liquid is available for hydrating the flour proteins to develop gluten. While melted, toast the milk solids for a few extra minutes until you can smell a butterscotch aroma.

When making brown butter, the solids change color and develop hundreds of new flavors. The process happens quickly, so keep a close eye on appearance change and your nose to indicate doneness. Immediately transfer to a large bowl to halt the cooking process.

Use two types of sugars
Yes, sugar adds sweetness to cookies, but that’s not all. I use granulated sugar for a pure sweet flavor. Plus, it helps to crisp the edges of the cookies because the crystalline structure doesn’t dissolve as much.

For a molasses flavor, add dark brown sugar. It’s also great for attracting moisture from the environment because it’s a humectant, keeping the centers slightly moist.

The ratio of oat to flour is critical. I use 3 parts oats to 1 part flour to ensure a chewy texture instead of a dry and cakey structure. Using unsaturated fat like vegetable oil and melted butter keeps the batter denser. A whole egg plus an egg yolk helps with binding and moisture, which is needed since I only use a tiny amount of flour.