Preheat your oven to 190°C/ 170°Fan /Gas 5 /375°F.

You will need one or two baking trays, either non-stick, lined with baking parchment, or lightly greased with extra butter.

Put the oatmeal, flour, sugar, and salt in a bowl and stir together.

Coarsely grate the butter into the mixture (dip the butter into the flour now and then if it sticks to the grater) then use your fingertips to rub it in until the mixture looks like breadcrumbs.

Using a fork, stir in enough of the beaten egg to make a soft dough: you may not need all of the egg. As the mixture starts coming together, switch to your hands to form it into a smooth ball.

Generously sprinkle your work surface or a silicone mat with extra wholemeal flour. Transfer the dough onto it and flatten slightly with your hand.

Sprinkle a little more flour over the top then roll out 2 - 3 mm for thinner biscuits, up to 5 mm for thicker biscuits.

Cut into what shapes and size you would like and transfer them to the prepared tray.

Gather up the scraps of dough, re-rolling to make more biscuits until all the dough is used up.

Optional and for decorative purposes only: use a fork, skewer or cocktail stick to make a pattern of holes.

Transfer the tray(s) to the preheated oven and bake until cooked through (approx. 15 - 20 min). If necessary, turn the tray(s) around half way through for even baking.

Transfer the biscuits to a cooling rack until completely cold before storing in an airtight container for up to 1 month.