If I could only make one category of baked good for the rest of my life, it might be pastries. It’s a bit of a cheater answer, though- pastry doughs are pretty variable, and include things like crumbly doughs reminiscent of shortbread and sugar cookies, flaky pies, shatteringly crisp puff pastries, and rich, slightly chewy croissants and danishes.
The various types of doughs have slightly different proportions and can benefit from different flour types and other ingredients like egg and sugar, but in my eyes the difference comes down to the fat.
Fat (usually butter, in my kitchen) is responsible for most of the texture in pastries, and it has a lot to do with how it interrupts the structure of the dough. Fat interferes with gluten’s ability to form networks- gluten strands can’t link up when there’s fat in the way, and this contributes to both tenderness and flakiness depending on how finely the fat is added to the dough.
In crumbly pastries like shortcrust and pate brisee, the butter is thoroughly incorporated into the flour. By the time wet ingredients are added (gluten forms from proteins in the flour in the presence of water), the bits of flour can’t form big gluten networks in the whole dough mass because they get interrupted by the fat. Ingredients like eggs can add to the structure with their own proteins but without the springiness of gluten. Crumbly doughs tend to bake up crisp and with fine crumbs, since the fat prevents most of the gluten from linking up with itself and holding together in large chunks.
Flaky Pie Dough
In flaky pie doughs, a lot of similar things happen with the fat but on a bigger scale. There are multiple ways of working the fat into the flour but the fat is generally left in chunks- the larger the chunks, the bigger the flakes will be. Pie doughs tend to be mixed as little as possible and then periodically rested in the fridge. Resting them after mixing allows the water to hydrate the flour, but also firms up the fat. When pie dough is rolled out, two major things happen (aside from the dough becoming flatter, of course): gluten gets developed because the dough is being worked, but the firmed up chunks of fat are flattened into thin sheets within the dough. This means that the dough gains a bit of strength, and that the thin sheets of fat form layers within the dough that block networks of gluten from one another. When the dough gets baked, these layers of dough set individually- the fat keeps them separate from one another, creating flaky layers.
Puff pastries take that flaky texture to a whole new crispy level- rather than mixing the fat in while forming the dough, the dough is made separately and then wrapped around a flat block of fat. Multiple iterations of rolling the dough out thinly, folding, and rolling again make a staggering amount of extremely thin layers. These doughs are called laminated doughs. In this case, the dough is strong in terms of gluten, but because of the fat the layers become so thin that they’re crisp and brittle once baked. The fat (as in the other doughs) allows for separation but also air pockets- the water in the dough creates steam during baking, which expands the dough and allows it to rise. Separating the layers, the fat allows for large air pockets to form, and gives rise (hah) to a light, delicate texture once the layers set in place. Phyllo works similarly, but the dough itself is rolled thinly first and then brushed with liquid fat, rather than adding fat and rolling them together.
Laminated Bread Doughs
Toeing the line between pastry and bread are things like croissants. They’re laminated like puff pastry but the base is a yeasted bread dough. The doughs are various levels of enriched (having additions like sugar, fat, and eggs)- from slightly enriched croissants, to comparatively rich and sweet Danishes, to nap-inducing laminated brioche. They’re a little more difficult to make than puff pastry, since you have to account for yeast activity and keep the consistency of the dough and butter the same, but the fat works the same way in these. Really, they get their own mention here not because the concept is different but because I really like them. The yeast in the bread gives flavour and lift, while the fat allows for an even higher rise (as more steam gets captured within the thin layers of dough) and even more flavour. When done right, the outer texture is flaky like puff pastry but the inside is almost impossibly airy thin layers of rich bread.
A short note on which fats to use for pastry: I use butter pretty universally, unless there’s a recipe that specifically calls for a different type of fat. Shortening generally gives pastries a better texture, but I find the taste of butter is worth it. Lard is more difficult for me to find, so I don’t tend to use it at home. Note that butter is only about 80-84% fat- the rest is milk solids and water, so the different fats don’t always sub 1:1 (margarine is made with that in mind, so it’s a better sub for butter). The water content can be important in recipes, especially ones that don’t have much in the way of wet ingredients- this moisture can help the dough come together and also contribute to steam while baking to create rise.