In a saucepan over medium to medium-high heat, melt the 1/3 cup of butter, swirling occasionally until it has browned and is nutty smelling. Pour the butter into the mixer bowl and let cool to room temp.
Begin preheating the oven to 350° F (176° C) and prepare a 12 well muffin tin by greasing and flouring with a light hand. Alternately, spray with baking spray that contains flour or use a thoroughly nonstick pan.
Once the butter has cooled, add the sugar and egg then beat until it’s a pale yellow and super creamy, around 3-5 minutes.
While the mixer is creaming, assemble the dry ingredients in a bowl including the zest if using. After the butter mix is well creamed, set the mixer to low, add a third of the dry ingredients, then half the milk, alternating between the two and blend until just mixed. Give a few final stirs with a spatula by hand.
Using a soup spoon, split the batter between the muffin tin wells and bake for about 20-25 minutes, until the puffs are lightly golden. About halfway through baking, melt the remaining butter then add the cinnamon and sugar to separate bowl, stirring to combine.
Let the puffs cool slightly then turn them out onto a cooling rack. Roll each puff in the melted butter then roll each one in the cinnamon sugar mix, setting them on the cooling rack to cool.
Serve warm immediately or store in a sealed container and serve at room temperature or reheat briefly to serve.