How to Make It
Preheat the oven to 350°. Butter and flour a 10-cup Bundt pan. Spread the walnut halves in a pie plate and toast for about 8 minutes, until golden brown. Let cool, then coarsely chop.
In a medium bowl, whisk the flour with the cinnamon, baking powder, baking soda and salt. In a large bowl, using a handheld electric mixer, beat the butter until creamy. Beat in the sugar and vanilla until fluffy. Beat in the egg yolks, one at a time, then beat in the crème fraîche. Beat in the dry ingredients at low speed. Fold in the walnuts.
In a clean bowl, using clean beaters, beat the egg whites until firm peaks form. Beat one-third of the whites into the batter, then fold in the remaining whites until no streaks remain. Scrape the batter into the prepared Bundt pan and smooth the surface with a spatula. Bake in the middle of the oven for about 50 minutes, until a toothpick inserted in the center of the cake comes out clean. Let cool in the pan for 20 minutes, then invert the cake onto a rack and let cool completely.
Whisk the confectioners' sugar with the half-and-half and cinnamon. Pour the glaze over the cake, allowing it to drip down the side; let cool until set before serving.