Estonian recipes: Condensed Milk Cookies (kondenspiimaküpsised)

I'm continuing with sharing Estonian recipes with you this month, in anticipation of the national holiday later this month. Here's a small baking project for the weekend - small, delicious and crispy-tender condensed milk cookies. The recipe is adapted from a classic Estonian cookbook "Valik toiduretsepte" (the 1974 edition), where they're called simply "milk cookies". The sweetened condensed milk gives those cookies not only a desired sweetness, but also a slight dulce de leche flavour, which I find very appealing.

Condensed Milk Cookies
(Kondenspiimaküpsised)

250 g all-purpose/plain flour
1 tsp baking powder
a pinch of salt
1 tsp vanilla sugar or vanilla extract
150 g cold butter, cubed
175 g sweetened condensed milk
2-3 Tbsp water

a small egg whisked with some water, for brushing

Mix the dry ingredients (flour, baking powder, salt, vanilla sugar) in a bowl, then add the cold cubed butter. Using a knife, cut the butter into the flour mixture, until it resembed wet crumbs. Now add the condensed milk and using your hands, knead into a ball (you may not need the water at all).
Place the dough into the fridge for half an hour, so the gluten can relax a little.
On a lightly floured surface, roll out the dough until 3-4 mm thick (1/8th of an inch). Cut into shapes (I cut into diamonds, using a roller cutter).
Transfer the cookies into a lined baking sheet and brush with an egg wash.
Bake in a preheated 200 C / 400 F oven until light golden brown.