Preheat oven to 350°F. Generously butter 9-inch cake pan with 2-inch-high sides. Dust pan with cornmeal, tapping out excess. Sift flour, 1/2 cup cornmeal, baking powder, and salt into medium bowl. Using electric mixer, beat butter in large bowl until smooth and fluffy. Beat in orange peel. Gradually add 1 cup sugar and beat until light and fluffy, occasionally scraping sides of bowl. Add eggs 1 at a time, beating well after each addition. Beat in sour cream and vanilla. Fold in dry ingredients in 3 additions until just incorporated. Transfer batter to pan; smooth top. Sprinkle with crushed sugar. Bake cake until tester inserted into center comes out clean, 25 to 30 minutes. Cool in pan on rack 10 minutes. Run knife around pan sides to loosen. Turn cake out onto plate, then invert, crushed sugar side up, onto rack. Cool completely. DO AHEAD: Can be made 8 hours ahead. Wrap in foil; let stand at room temperature. Cut cake into wedges. Serve with Buttermilk Ice Cream and Rhubarb Compote alongside.