Hazzelnutbuterkoeke or hazelnootboterkoek or Hazelnut and butter coffee cake

Why I Love This Recipe
This cake we used to eat at home in the weekends, it's delicious with coffee. It is quite a filling cake. I found the recipe some time ago in a cookingbook called "Nije petiele", it has frisian recipes collected by Wieke de Haan and was published in 1993. The book is written in Frisian, so I made a translation of the recipe below.
The hazlenuts can be substituted by the same amount of wallnuts, if you don't have hazlenuts at hand. Though personally I prefer to use hazlenuts.
Ingredients You'll Need
225 grams of flower
200 grams of unsalted butter [the real stuff], cut into small pieces
175 grams of soft brown sugar
100 grams of ground hazelnuts
50 grams of whole hazelnuts
half an egg, beaten
pinch of salt
Directions
1 Preheat the oven at 180 Celsius or 350 Fahrenheit
2 Mix flower, sugar, ground hazelnuts and salt, put in the pieces of butter and mold it into a dough
3 Place the dough in a greased cake or pie pan [diameter 24 cm or 9.5 inches]
4 Decorate with the whole hazelnuts by pushing them half into the dough
5 Brush with the beaten egg
6 Bake in the middle of the oven for about 40-45 minutes
7 The cake is done when a toothpick tests clean, take it out and leave to cool in the pan
8 Once cooled of use a knife to seperate the edges of the cake from the pan and serve still a bit warm or cold