Line 2 baking sheets with baking parchment. Grind the caraway seed to a powder in a small electric grinder or in a pestle & mortar.
Place the ground caraway seeds, flour and five spice powder in a bowl and add the butter. Rub the butter into the flour mixture until it resembles fine breadcrumbs, then stir in the sugar and lemon zest.
Make a well in the centre and add the eggs. Use a fork whisk the eggs to break up then start to incorporate the flour. Finish mixing to a dough with your hands.
Divide the dough into 6 balls weighing 65g and 4 balls weighing 85g. Place the dough balls on one of the baking sheets, cover with clingfilm and chill for 30 mins.
Preheat the oven to 180℃ /160℃ fan/gas mark 4. Knead the smaller pieces of dough on a lightly floured surface and roll into a 30cm rope. Tie into in the rope then shape into a double knot by tucking one end of the rope on top and the other underneath.
Shape the remaining pieces of dough into Celtic knots. – Do this in two pieces. Take off about a 1/4 of each piece and roll the larger piece into a long rope about 45cm long. Shape into the base of the the knot and place on the second baking sheet. Roll the remaining piece of dough into a rope and place in a circle on top of the base, of the knot.
Brush the biscuits with beaten egg and sprinkle with caster sugar. Bake the Celtic knots for 15 – 20 minutes, until golden brown and the double knots for 20 – 25 minutes.
Remove from the oven and leave to cool on a wire rack.