Preheat the oven to 180C/160C Fan/Gas 4. Line three baking trays with baking paper.
To make the biscuit dough, measure the butter, sugar, flour and semolina into the bowl of an electric food mixer and mix until a soft dough is formed, taking care not to over-beat. Alternatively, add the butter and sugar to a mixing bowl and beat with a wooden spoon until soft and creamy, then stir in the flour and semolina. Divide the dough evenly into three and dust your work surface with flour before kneading each batch.
For the chocolate chip biscuits, knead the chocolate chips into one portion of dough, shape into 20 balls and arrange, spaced well apart, on one of the baking trays. Press down with the back of a fork into discs about 5cm/2in in diameter and bake in the oven for 10â€“12 minutes, or until golden-brown.
For the lemon biscuits, knead the lemon zest into the second portion of dough. Roll into a long sausage shape (about 20cm/8in long) and roll in the demerara sugar. Wrap in cling film and leave in the freezer for about 30 minutes, or until firm and nearly frozen. Slice into 20 even rounds, each about 1cm/Â½in thick. Arrange on a baking tray, spaced well apart, and bake for about 10 minutes, or until pale golden-brown.
For the almond biscuits, knead the almond extract into the remaining portion of dough, along with most of the flaked almonds. Shape into 20 small balls and arrange on the third baking tray, spaced apart. Place a few almonds on top of each ball of dough and press flat with the back of a fork into discs about 5cm/2in in diameter. Bake for about 10 minutes, or until golden-brown.