Beat the butter and powdered sugar until fluffy at high speed, about 10 minutes.
Lower the speed, then add the egg yolks one at a time. Beat until smooth then add sweetened condensed milk, shake until smooth.
Sift flour, powdered milk and speck seasoning, gradually add to beaten egg, stir again with a spatula until smooth.
Put 1 tablespoon of vegetable mixture into a 20 x 20 x 7 cm tin which has been lined with parchment paper, flatten it out. Oven over low heat at 180°C until browned, remove from oven then press down on the surface with the back of a spoon or a layer cake presser.
Pour 1 tablespoon more of the dough, flatten, oven with high heat until browned, press the surface again. Repeat these steps until the dough runs out.
6. After the last dough, bake with low heat for 15 minutes until cooked. Once cooked, remove from the oven, cool and then cut into pieces.