1Start with the jam. Place a small plate in the fridge. Pick through the blackberries, discarding any remaining leaves or twigs.
2Place the fruit in a preserving pan or heavy-bottomed saucepan with the jam sugar, lemon juice and peppercorns. Set over a medium heat to come to the boil, then reduce the heat to a simmer for 15 minutes.
3Remove the plate from the fridge and spoon a little of the jam onto it and return it to the fridge for a minute. Push the jam on the plate with your finger; it should wrinkle when it is ready. Remove the pan from the heat and set aside.
4To make the doughnuts, put the flour, caster sugar, salt, eggs, lemon zest, water, yeast and pepper into the KitchenAid® Artisan ® Mini Mixer bowl and turn the speed to 8 until the dough starts to form a ball and is coming away from the edges of the bowl.
5Now turn the speed down to 5 and slowly add the soft butter, a little piece at a time, until it is all incorporated and the dough is glossy, smooth and very elastic when you pull at it.
6Cover the dough and leave it out until it doubles in size. This will take approximately 2 hours, depending on how hot the kitchen is.
7Knock back the dough, recover the bowl and place in the fridge overnight.
8Pour the oil into a large, heavy-bottomed saucepan and set over a medium heat. Use a kitchen thermometer to heat the oil to 180C.
9Remove the dough from the fridge and roll it into a sausage – ideally roll it out on a marble board or surface but otherwise on a cool work surface. Cut the length into 18g portions, giving each a quick, light roll to make a ball.
10Lightly oil and flour two large baking trays. Line the balls of dough across the trays, well spaced as they will expand. Cover loosely with cling film and leave for up to 4 hours until doubled in size.
11Using an oiled scraper, add the doughnuts one by one to the hot oil. Don’t over crowd the oil and make sure you turn them evenly until golden, which should take a minute on each side.
12Tip the granulated sugar into a deep tray. Transfer the doughnuts to the sugar tray whilst they are still hot and oily, giving the tray a shake to cover each doughnut in sugar.
13Once they are cool enough to handle, make a small, deep cut in the side of each doughnut. Fill a piping bag or squeezy bottle with the jam, place the nozzle in the cut and fill each generously with jam. Best eaten warm.