Place the butter in a small saucepan over a low heat. If you can, use a saucepan with a light coloured bottom, so you can see how the butter is browning. Stir and swirl intermittently for about 5 or so minutes, until the butter foams and then forms medium to dark brown flecks in the bottom of the pan. See the picture for reference on what colour the specks should be. Take it off the heat as soon as it’s done, because it will continue cooking.
Working quickly, place a medium sized metal bowl on your kitchen scale, and pour in the hot melted butter. A medium sized bowl makes it easier to stir the flour in later. On the note of equipment, you’ll be using the saucepan again, so don’t put it in the sink.
Measure the 1 tablespoon and 3 teaspoons of milk into the warm saucepan and swirl around. This has three benefits – firstly, less dishes. Secondly, it will warm up the milk using residual heat, so that the milk doesn’t cause the butter to harden when you pour it in. Thirdly, it will pick up the extra brown butter bits on the bottom of the pan. The more the merrier.
Tare off the scale (reduce it back to zero) so you can weigh in the sugars. Remove from the scale, stir to combine, and add the vanilla bean paste. Finally, stir in the warmed soy milk, and keep stirring until it is thoroughly combined and thickened slightly, around 1-2 minutes.
Allow the butter mixture to sit and thicken for 5 or so minutes while you weigh out the flours in a small bowl. Add the baking powder and fine salt to the flours, and use a whisk to thoroughly combine.
Add the flour to the butter mixture, and use a spoon to thoroughly combine. Make sure you get every little bit of flour off the side of the bowl. It will take a little while to incorporate all the flour, but don't stop until you have. A little good old fashioned elbow grease will get you there! The mixture should be matte but kind of shiny, and hold it's shape reasonably well. Transfer it to the fridge to harden for at least 2-3 hours, ideally overnight. See notes for my findings on letting the dough rest.
To bake, heat the oven to 180 degrees Celsius, or 356 degrees Fahrenheit. Line 2 baking trays. Working quickly, use your hands to form 10-12 even sized small bowls of dough, and place 4 on a sheet. If it's hot where you are you can flash freeze the dough for 10 minutes, but see the notes first.
Bake the cookies for 10-12 minutes, or until browned and wrinkly. Allow to cool completely before removing from the tray. Finish with a little sprinkle of sea salt (it amplifies the taste!) and store, cooled, in an airtight container.