Place the dry ingredients in a large bowl with 1½ teaspoons sea salt, stir to combine then make a well in the centre.
Crack the eggs into a small bowl and beat. Next, pour in 1½ tablespoons of oil and 350ml water into the well and add most of the beaten egg (saving a little for egg washing later). Mix with a fork, then bring together with your hands to form a ball.
On a lightly dusted surface, knead the dough for 10 minutes until smooth and springy. Be careful not to add too much flour here to prevent the dough drying out.
Place in a large oiled bowl, cover with a damp tea towel and leave to rise in a warm place for 1 hour, or until doubled in size.
To braid your challah, divide the dough into two balls. Put one aside covered with a damp tea towel and cut the other ball into 4 even pieces. Roll each piece into a thin sausage-shape, roughly 60cm long.
Place two of the strands next to each other vertically. Weave the remaining two strands horizontally over and under the vertical strands to form a cross shape.
Working with the top pair of strands, take the strand that is underneath and place over the strand next to it. Do the same with the next pair of strands and continue this around the cross. Once all four pairs have been crossed over, do the same in the reverse direction – clockwise/anti-clockwise depending on your strands. The rule to go by is to always place the underneath strand over its pair.
Continue this process until you have used up the dough. As you start to run out of dough tuck the ends under the loaf to form a neat braided ball. Place on a lined baking tray.
Repeat the braiding technique with your second ball of dough.
Cover both loaves loosely with a damp tea towel and leave to rise for a further 30 minutes. Preheat your oven to 180°C/350°F/gas 4.
Use the remaining egg to glaze the challah. Sprinkle over the sesame seeds and bake for 40 minutes, or until golden. Adding extra egg wash halfway, if needed.