Heat oven to 180C/fan 160C/gas 4. Grease a 20cm loose-bottomed cake tin and line the bottom with baking parchment. Mix the flour, caster sugar and cinnamon together with a pinch of salt in a bowl. Whisk the butter, egg yolks and milk together and combine with the dry ingredients to make a soft dough. Turn out onto a floured surface and roll out to a rectangle, about 30 x 25cm.