From what I can tell testing brownies over the years it seems like the common denominator to getting the shiny tops is making sure the sugar is well dissolved. Whether you whip your eggs and sugar, or stir sugar into HOT melted butter, you should get a shiny top. However sugar dissolves in water, not fat, so I would opt to mix it with the eggs since they have a higher water content than butter. So the method I use is mixing eggs, sugar and salt on high speed until white and fluffy, then adding the hot melted butter/cocoa and or chocolate mixture to help to continue melting the sugar, then adding flour last.

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