Sweet Potato Pound Cake with Cinnamon Sauce

Cake:
1 1/2 cups cake flour
1/2 teaspoon baking soda
1/2 teaspoon salt
1/2 teaspoon ground cinnamon
1/2 teaspoon ground nutmeg
1/2 cup unsalted butter (at room temperature)
1/2 cup sour cream (at room temperature)
1 1/4 cups plus 2 tablespoons granulated sugar
3 eggs (at room temperature)
1 (8 ounce) sweet potato, baked, peeled and pur ed
1 teaspoon vanilla extract

Heat oven to 300 degrees F. Lightly oil an 8 1/2 x 4 1/2-inch loaf pan.

Sift first 5 ingredients into medium bowl. Using an electric mixer, beat butter and sour cream in large bowl until well blended. Gradually add sugar and beat until mixture is light and fluffy. Add eggs 1 at a time, beating well after each addition. Mix in 1/2 cup sweet potato pur e and vanilla extract. Stir in dry ingredients. Transfer to prepared pan. Bake until tester inserted into center comes out clean, about 1 hour 15 minutes. Cool cake in pan on rack for 30 minutes. Cut around sides of pan with knife. Turn cake out onto rack and cool.

Cinnamon Sauce:
2 cups milk
3 cinnamon sticks, crushed
1/2 vanilla bean, split lengthwise
4 egg yolks
1/2 cup granulated sugar
1/4 cup sour cream

Combine milk and cinnamon sticks in heavy medium saucepan. Scrape in seeds from vanilla bean; add bean. Bring to boil. Remove from heat. Cover and let steep 15 minutes. Whisk yolks and sugar in bowl to blend. Slowly beat milk mixture into egg mixture. Strain custard into same saucepan. Cook over medium-low heat until custard thickens and leaves path on back of spoon when finger is drawn across, stirring constantly, about 15 minutes; do not boil. Pour custard into bowl. Whisk in sour cream. Cover and chill until cold, stirring occasionally. (Can be prepared 1 day ahead.) Cut cake into slices and transfer to plates. Top with praline or toffee ice cream and sauce.