Two Cups Flour

Make Brown Butter
18 Place 260 grams of butter into a medium light colored saucepan on medium heat. As the butter browns it will lose water content, leaving you with a lower volume of brown butter at the end. 
22 Once the butter melts, continue cooking, swirling the pan occasionally, for about 5–8 minutes, until the butter foams and the milk solids separate to the bottom turning golden brown with a nutty aroma. I like to use a silicone whisk or spatula to stir the butter as it browns.
23 Remove from heat and immediately whisk in the milk powder.
24 Stir for 30–60 seconds, until the mixture turns a deep golden color and smells toasty.
25 Set aside to cool, so that it re-solidifies into a softened butter texture. Do Not use melted butter in the frosting. Place the brown butter in the fridge to speed up the process. Or make ahead and keep at room temperature. 
Double Broiler
0 Separate the eggs whites and place them into the clean metal bowl of a stand mixer. *You can use a separate large metal mixing bowl, but I find it easier to just use the bowl of the stand mixer and then move forward with whipping.
1 Add both of the sugars to the egg whites. Create a double boiler by placing the bowl over a pot of shallow simmering water. Do not let the mixing bowl touch the hot water.
3 Whisk the egg whites and sugar continuously until the temperature on an instant thermometer reads 160℉ (72℃). You can also check by carefully dip your finger into the hot sugar and rub the mixture between your fingertips. If you don't feel any grains of sugar, the mixture is ready. (about 6-8 minutes)
Whip Meringue 
4 Remove the mixing bowl from the heat and wipe the bottom of the bowl dry with a towel. Place the bowl on the stand mixer.  Using the whisk attachment start whipping on high speed.
5 Continue to whip until a thick, glossy and marshmallow like meringue with stiff peaks is formed. Test by lifting the whisk from the meringue, stiff peaks will hold their shape. The bowl should be cool or at least room temperature to the touch. (about 8-10 minutes)
7 While mixing on medium speed drop in one tablespoon of the softened and browned butter at a time into the whipping meringue. Wait for each piece of butter to mix-in before adding the next. 
9 You may notice the meringue losing its stiffness and becoming softer almost soup-like, that’s ok, keep adding butter.
10 Once half of the butter has been mixed in, stop the mixer and scrape the bottom and sides of the bowl with a silicone spatula to grab any stuck meringue or bits of butter. We want all the butter to emulsify with the meringue.
11 Continue mixing and add in the remaining butter.
12 The meringue may deflate and look runny or split, but keep mixing for another 10-15 minutes after all the butter has been added on medium speed.
13 If after 10 minutes of mixing it hasn't magically transformed into a frosting texture, just place the bowl in the fridge for 10 minutes with the paddle attachment. Then, whip again until silky smooth.
14 Once the buttercream looks like a spreadable frosting add in the vanilla bean paste and salt, then give it a couple spins on low to mix.
Smooth Frosting
16 If there are a bunch of air bubbles in the frosting, mix on low speed with the paddle attachment until smoother for about 10 minutes. Or simply take a silicone spatula and beat the frosting left and right in the bowl, by hand to loosen up an air bubbles.