Preheat the oven to 180 degrees and line a baking sheet with baking parchment.
Place the sugar and butter in the bowl of your stand mixer and whisk until light and fluffy.
Add the flour, baking powder, treacle, vanilla essence, cinnamon and egg yolk and continue to combine until the mixture forms a soft smooth dough.
Slice the dough into two equal parts and roll them out into sausages as long as your baking sheet.
Laying the sausages on the sheet then press the dough down gently with your fingers so it measures roughly 10cms across.
Brush the egg white over both flattened sausages.
Sprinkle pearl sugar over the dough, finishing off with a scattering of flaked almonds.
Bake for 10-12 minutes until the top is starting to look drier.
While the biscuits are still warm, use the tip of a sharp knife to gently score the join between the sausages if they’ve joined together. Cut each sausage into slices roughly 2cms wide, angling them slightly so they are slanted.
Allow to cool before dividing the biscuits and serving; they will last a good two weeks in a biscuit tin, but the dough can be frozen very nicely so you could always bake one sausage and freeze the other!