Cream butter and sugar. Beat in yolk and vanilla, then beat in flour in 3 batches. Turn out, knead into ball, refrigerate 1 hr. Roll out into 5mm/0.2" thickness, cut out 7cm/2.8" rounds (24 pieces). Brush with egg wash, score cross design with fork, bake 15 min @ 180°C / 350°F (160°C fan).

Cream butter & sugar - Place butter in a bowl and beat for 30 seconds using an electric beater on low speed. Then add sugar and beat for 1 minute on medium until fluffy and slightly paler in colour.

Beat in egg yolk and vanilla, just until combined then stop beating.

Make dough - Add 1/3 of the flour to the mixture and mix still using the beater on medium low speed. Once incorporated, add half of the remaining flour then mix and repeat with the remaining flour. It will resemble like wet sand. Turn out onto the work surface and use your hands to bring it together, then knead it into a smooth ball of dough.

Rest - Wrap in cling film and refrigerate for 1 hour. (Note 4)

Preheat oven to 180°C / 350°F (160°C fan-forced).

Roll - Using a rolling pin, roll the dough between two sheets of baking paper / parchment paper to 5mm / 0.2" thickness. It doesn't matter what shape it rolls out to as long as it's the correct thickness.

Cut - Using a 7cm / 2.8" round cookie cutter, cut out the galletes. Use a spatula to transfer them onto 3 baking paper / parchment paper lined trays. Re-roll scraps and repeat until all dough is used - you should get 24 biscuits. (Note 5)

Egg wash - Mix together egg yolk and milk then brush the galettes lightly with the egg wash.

Decorate - Dip a fork in water and use the back of the fork to lightly scrape a cross on the surface of each biscuit, lightly etching a line into the dough, not just the egg wash (watch video, it's helpful).

Bake 2 trays for 14 - 15 minutes until the biscuits are lightly golden (watch the top tray as it might brown faster). Once they are done, bake the 3rd tray.

Cool - Leave biscuits on trays for 5 minutes, then transfer to a rack to cool completely.