Melt butter in a small saucepan over the stovetop.

Place evaporated milk in a large microwaveable dish/glass measure cup. Microwave for 60 seconds or until boiling.

Add sugar to the evaporated milk immediately after removing from the microwave. (It will puff up when you first add the sugar to the milk, so that's why you want a big container to stir it in.)

Whisk sugar and milk for a minute until sugar is mostly dissolved. Add to melted butter on the stove and whisk continuously over medium-high heat. Continue whisking until the syrup boils and thickens up (happens when it reaches a boil.) Don't cook too long or it will caramelize the sugars and it won't be that blonde butter syrup you want.