Preheat the oven to 350°F and line a baking tray with parchment paper or silicone mat.

Whisk together the egg, caster sugar and vanilla sugar. Make sure your egg is at room temperature.

Pour the beaten egg into a bowl with peanut butter, add baking soda and a pinch of salt, and whisk together until well-combined and uniform.

Scoop out the batter with a spoon and roll into 8 small balls.

Transfer balls onto a baking tray and press lightly with the back of a fork to create a criss-cross pattern. Make around 10-12 cookies.

Let them bake in a preheated oven for 8-10 minutes.

When baked, leave them in a tray for 3-4 minutes, then place onto a wire rack to cool completely.

Serve and enjoy!