We started with a traditional rolled and cut biscuit dough and treated the butter three different ways. For the first sample we used the most common method of incorporating butter: We cut cold butter into the flour (using a food processor) until it resembled pebbly pieces. We also made a batch with melted butter and another where we cut thin slices of cold butter and pressed them between well-floured fingers until they resembled nickels. We formed identical doughs with each batch from which we then rolled and cut biscuits.
A post-baking lineup told the whole story. The melted-butter biscuits sat squat, dense, and uniform next to the moderately flaky traditional biscuits, both of which paled in comparison to the height and flakiness of the biscuits made with the thin pieces of butter.
The key to making flaky biscuits is to get layers of solid fat spread between the layers of dough. This way, the thin layers of fat (butter) will melt when they hit the hot oven. And because butter is part fat and part water, the water turns to steam, filling the now-empty spaces between the dough, and giving rise to flaky layers.
Melted butter, on the other hand, is incapable of forming discrete layers of solid fat between layers of dough; this is why our biscuits made with melted butter turned out dense and flat. Similarly, the standard pebbles of butter can't begin to form layers of fat between layers of dough until they soften enough to spread out. Even when they do start to spread in the oven, the softening pebbles can't spread far enough, forming only small regions of fat that will not give rise to much flakiness at all.
The lesson? If flaky biscuits or pastries are what you desire, be sure to use techniques like lamination, the process of repeatedly rolling and folding the dough over itself, or fraisage, where you smear the dough with the heel of your hand, to get thin, long layers of solid fat in the dough.