Using your food processor when making shortcrust pastry is dead easy and super quick. It's a particularly good technique to use when the weather is warm, or you have warm hands, as the butter is less likely to soften and melt while making the pastry.
To make shortcrust pastry in the food processor, follow these three simple steps:

1. Put the flour, salt, chilled butter and sugar (if the pastry is sweet) in the bowl of your food processor. Use the pulse button to process until the mixture resembles coarse breadcrumbs.
2. Sprinkle over the water/whisked egg yolk (you’ll generally find that you need a little less than if making the pastry by hand) and then use the pulse button to process briefly until the mixture just starts to cling together. Don’t let it get to the stage that it forms a ball as you may overwork the pastry and make it ‘tough’ when baked.
3. Turn the pastry out onto a lightly floured, cool bench top and bring it together with your hands. Lightly knead the pastry with your fingertips for about 10 seconds or until comes together but isn’t completely smooth. Shape the pastry into a disc, wrap well in plastic wrap and place in the fridge to rest for 30 minutes or as directed in the recipe.

Most stand mixers are now sold with a range of attachments made for specific mixing jobs, including a 'paddle' one. This is what you need to use to get the best results if a recipe asks you to beat, mix, cream or combine your ingredients 'using an electric mixer'. It's not meant for 'whisking' (when you are making meringue for example) or for 'kneading' bread doughs - use the whisk or dough hook attachments for these jobs.