I had a cookie recipe for a taste of children to take home. Looking at the pictures on the net I came across two-colored cookies that I found really nice. I took the idea by adapting the recipe with my own habits.

I tested several recipes. I give you now my favorite version. 
This recipe is very quick to perform, less than 30 minutes, cooking time range, enough to taste a small improvised.

for 20 cookies around (depending on size) 
150g brown sugar 
100g butter 
1 egg 
200 g flour 
1 teaspoon baking powder 
100 g chocolate chips (or crushed chocolate for me) 
1 pinch salt 
1 pinch of vanilla extract 
1 tablespoon unsweetened cocoa

In a bowl, put the butter cut into cubes. It is better to be a little soft. 
Add brown sugar, salt, vanilla. Mix with a fork (mash the butter with a fork to incorporate the sugar) 
Add egg, continue mixing with a fork. 
Add the flour, baking powder. 
Pour half of chocolate chips or crushed chocolate and stir to incorporate them into the dough. 
the dough should not be too closely linked, it must have a sandy appearance. 
Separate into two pulp and add in a bitter cocoa and mix with a fork and then with your fingers. 
Make small balls and assemble a black ball of dough and a white ball of dough. 
Place the two-color balls of dough well apart on a cookie sheet lined with parchment paper. 
Add on top the rest of the chips. 
Bake oven preheated to 180 ° 
Bake for 10 to 15 minutes (depending on size of cookies) 
I 20 shaped cookies with this paste and I cooked for 13 minutes.

  

They are soft and crispy. 
You can put butter half salt instead of sweet butter or some sweet butter to bring a little touch of flavor, do not put a pinch of salt in this case.

I made a first batch with white sugar and crushed chocolate, the result is visually attractive because cookies are lighter but are less crispy, more melting. Children preferred the second version of the same if they had loved the first.

bicolour white sugar cookies

If your butter is not soft, cut it into small plots, overwriting the butter with a fork it will blend easily. I use a fork to mix because it allows the dough to not be too homogeneous. I find that cookies are best when the dough is very homogeneous, with lumps.

Not to flatten the dough balls, it stretches slightly during baking. If the raw dough is too flattened cookies will not be swollen and bulging (you can even flatten less than the pictures and let the ball-shaped, they will flatten thereafter) 
For good cookies must a suitable cooking. If you cook too long they will be crunchy, crispy outside and in. 
For them to be soft in (chewy) and crispy outside must stop cooking when the cookies are still soft, they harden on cooling.