I have a long and tortured relationship with pastry, I have written about this before, no reason to bore you with it. Having overcome my irrational fear of pastry, I am learning and exploring. It is so much more fun when we leave our irrational fears behind.
I am using Mary Berry's basic sweet pastry as a base and working from there. Being from the American mid-west, putting an egg in pastry seemed strange, but it does add texture without making the pastry tough.
All of the pastry gods, say to keep the butter cold, chilled. Be careful to minimize the melting of the fat in handling. I ran across a tip recently, freeze the butter, and grate it. This way the butter is cold, and it is broken into smaller bits before you start blitzing in the flour. It works wonderfully.
I store extra butter in the freezer. Using this method, I don't have to remember to take the butter out of the freezer to thaw, but not get warm before I start. The mix is faster, the result is very good.
Try different butters. For daily use we buy mostly Kerrygold Irish Butter. We find it has a wonderful and consistent flavor. During COVID it was sometimes in short supply, at times out of stock, and the price went up to reflect that. I was forced to buy other butters (first world problems here.) I found a domestic, danish style cultured butter that makes great pastry. It lacks the flavor depth for table use, or cooking, but it makes a flakier pastry. So my advice, experiment.
The photo above, a Blueberry tart. Pre-bake the tart shell. The filling is a pound of fresh blueberries, half a cup of sugar, a couple of heaping tablespoons of corn starch (corn flour), and about 3/4 cup of brandy. Cook the filling over medium to medium high heat until the liquid forms a gel. Fill the par-baked tart shell, and bake in a 350-375 degree oven for about 30 minutes. Heavenly, and fruity.