Cake recipes: creaming butter or melted?
Texture is the difference. When you cream the butter and sugar together, you create tiny air bubbles through the mixture. This is why it starts out yellow and can turn almost white when you cream it a long time. The leavening in the cake makes these tiny bubbles bigger and you end up with a higher rising cake. Mixing in melted butter doesn't create as many bubbles, so you end up with a denser product, closer in texture to a muffin than to regular cake.
re: JK Grence the Cosmic Jester
Excellent answer that nailed the chemistry.
Read more here in two New York Times articles:
"Butter Holds the Secret to Cookies That Sing:
"Cold butter’s ability to hold air is vital to creating what pastry chefs call structure — the framework of flour, butter, sugar, eggs and leavening that makes up most baked goods.
Before Anita Chu began work on her just-published “Field Guide to Cookies” (Quirk Books), she was a Berkeley-trained structural engineer with a baking habit she couldn’t shake. One of her favorite cookies is the croq-télé, or TV snack, a chunky cookie she adapted from the Paris pastry chef Arnaud Larher. “There is no leavening to lift it, no eggs to hold it together,” she said. “It’s all about the butter.” Ms. Chu’s experience in design helped her with the demanding precision of pastry.
“Butter is like the concrete you use to pour the foundation of a building,” she said. “So it’s very important to get it right: the temperature, the texture, the aeration.”
Ms. Chu says that butter should be creamed — beaten to soften it and to incorporate air — for at least three minutes. “When you cream butter, you’re not just waiting for it to get soft, you’re beating air bubbles into it,” Ms. Chu said. When sugar is added, it makes more air pockets, she said.
And those air bubbles are all that cookies or cakes will get, Ms. Corriher said. “Baking soda and baking powder can’t make air bubbles,” she said. “They only expand the ones that are already there.”
"Flour, Eggs, Sugar, Chocolate ... Just Add Chemistry"
with a chart by Shirley Corriher:
"Understanding how a cake bakes
1) Mixing: Beating the batter creates tiny air bubbles.
Proteins: From eggs
Starch granules: From flour
Air bubbles: From mixing
Syrup of water and sugar
2) Baking: The batter expands to its full volume.
Proteins: Begin to unfold
Starch: Absorbs water and swells
Air bubbles: Leaveners release gas that expands the bubbles.
3) Final product: The fluid batter sets into a porous solid.
Proteins: Unfold and coagulate to maintain cake shape
Starch: Swells to final size and jells
Air bubbles: Become pores in cake"