German Butter Cookies​ ​ 德国酥饼 - not that successful :)

​Ingredients: ​(makes about 50 pieces) 

​125g premium unsalted butter (soften at room temperature)
​40g ​icing ​sugar (sifted) 
​1 teaspoon vanilla paste or extract (optional)​
​125g potato ​starch
​80g plain flour