Preheat your oven to 350°F (175°C). Grease a 8 x 8 inch square pan or 9-inch round cake pan with butter or cooking spray. Then lined with parchment paper for easier release
In a separate bowl, whisk together the flour, milk powder, and salt. Set aside
In a large mixing bowl, cream the butter and powdered sugar together until pale, light and fluffy. Beat in the eggs, and vanilla extract until well combined. Sift in the flour mixture to the butter mixture, stirring until just combined.
Pour the batter into a prepared pan. Smooth the top with a bench scraper if necessary to make sure the surface is smooth and flat
Use a pastry brush to gently and thinly brush the surface with egg yolk. Place some almond slices decoratively on top of the cake
Baking:
Bake in a preheated oven, middle rack, for 30 minutes or until a cake tester inserted into the middle comes out clean and the surface is nice golden brown
Cooling:
Let the cake cool down in the pan for 10 minutes and then gently lift it up by holding on to the parchment paper and transfer to a cooling rack to let it cool completely
Serving:
This cake is best served after 24 hours (I know you don't like to wait). If you serve it on the same day, the cake feels dry and does not have much flavor. You will be rewarded by moist buttery and dense cake if you are patient enough. The cake tastes even better as time goes IMHO