The dough:Heat the milk in a medium saucepan over low heat until it reaches about 100F (37 C).Remove from heat and sprinkle the yeast and a pinch of sugar.Let it sit until it becomes frothy, about 5 minutes.Beat the melted butter, egg yolk, and vanilla. Set aside.Combine the flour, sugar, and salt in the bowl of a stand mixer.Make a well in the center and pour in the yeast mixture and the melted butter mixture.Mix at low speed with the dough hook until the dough comes together in a thick and slightly sticky ball.Knead at medium speed until the dough comes together around the hook, about 6 minutes or until the dough is smooth and elastic, and springs back when pressed.Remove the dough from the bowl and shape into a ball.Butter the mixer bowl and return the dough to the bowl, turning to coat evenly. Cover with plastic wrap and let rise until it has doubled in volume, about 1 hour 15 minutes.The topping:In a bowl, cream the butter with the sugar and cinnamon until well combined.On a lightly floured surface, roll out the dough to a 12″ x 14″ (30 cm x 35 cm) rectangle.Place the longest side facing you.Spread the butter, sugar, and cinnamon mixture.Roll the dough into a tight cylinder.Cut the cylinder into 8 equal pieces.Butter a 9″ x 13″ (23 x 33 cm) baking dish.Place the dough pieces in the prepared baking dish, leaving space between each.Cover with plastic wrap and let rise until the dough has doubled in volume, about 40 minutes.Preheat the oven to 325F (160 C).Bake until the brioche is golden brown, about 35 minutes.Let cool in the pan for 15 minutes.The glaze:Sift the powdered sugar into a bowl, then whisk in the cream and melted butter. Mix well.Transfer the brioche to a large serving plate and drizzle with the glaze while the brioche is still warm.