Add your butter to a nonstick pot and allow to melt,add the corn and lower the heat,cover and allow to cook till it starts popping, then you should start stirring the pot to avoid burning

Continue stirring the pot while it is closed,till all corns have popped and turned white,remove from heat and immediately add sugar,flavor and milk, combine all

NOTE; I didn't add the sugar together with the butter because I noticed it makes the pop corn dark and a little sour as we all know when sugar takes more time over heat it becomes sour,this is the result I got when I first tried the butter and sugar method together

So to avoid this,you can try the first method,but it depends on how you like it,as you can now spot the difference, but I like mine to be White