4egg yolks(it is very important for the density of the filling that you not get any egg whites into this filling, I find it best to separate eggs with my hands)
combine all the dry ingredients (granulated sugar to kosher salt) in the bowl of a stand mixer fitted with a paddle attachment and mix on low speed until evenly blended.
leaving the mixer on low, add the melted butter and mix for 2-3 minutes until all the dry ingredients are moist..
add the heavy cream and vanilla and mix for an additional 2-3 minutes until all the white streaks from the cream have disappeared into the mixture. stop the mixer and scrap down the sides of the bowl with a spatula.
add the egg yolks, one at a time, mixing each into the mixture just to combine before adding the next one. mix on low speed until the mixture is glossy and homogeneous; being careful not to aerate the mixture