Preheat oven to 350 degrees. In a small saucepan over medium heat, bring milk to a simmer. Meanwhile, in a large bowl, combine sugar, yolks, and cornstarch. Slowly pour milk into yolk mixture, stirring constantly.
Melt butter, then stir in brown sugar, vanilla, coconut, and walnuts. Add to milk mixture and stir to combine. Evenly distribute filling between pie crusts.
Bake until filling is set and a skewer inserted into center of pies comes out clean, 30 to 45 minutes. Chill overnight before serving. Serve with blueberries and lightly sweetened whipped cream.