making crunchy biscuits

[UsainWho]

I have a recipe for bourbon biscuits but the biscuit ended up too soft:

3oz flour
2.5 oz butter
1 oz sugar
1 egg yolk
1 tbsp cocoa

What could I do to make them crunchier like a real bourbon? I bake them at 180 for about 15 mins. I am happy to take someone's guaranteed crunchy biscuit recipe and amend so feel free to post yours! Thanks.

I've not got the recipe book here, but my bourbon recipe had syrup in. So, I think I'd be tempted to try something likegood housekeeping recipe

Hopefully someone will be along with a tried and tested recipe soon

You could try replacing half an ounce to an ounce of flour with ground rice.

If you replace 1oz of flour with the rice in a shortbread recipe it makes it crunchier.