1. Prepare Cake: Preheat oven to 350°. Bake pecans in a single layer in a shallow pan 8 to 10 minutes or until toasted and fragrant, stirring halfway through. Cool completely in pan on a wire rack (about 30 minutes). Reduce oven temperature to 325°.
2. Beat granulated sugar and 1 cup butter at medium speed with a heavy-duty electric stand mixer until light and fluffy. Add eggs, 1 at a time, beating just until blended after each addition.
3. Stir together flour and next 5 ingredients. Stir together buttermilk and baking soda. Add flour mixture to butter mixture alternately with buttermilk mixture, beginning and ending with flour mixture. Beat at low speed just until blended after each addition. Add jam and vanilla, and beat just until blended. Stir in toasted pecans. Grease (with shortening) and flour a 10-inch (12-cup) Bundt pan. Pour batter into prepared pan.
4. Bake at 325° for 1 hour to 1 hour and 15 minutes or until a long wooden pick inserted in center comes out clean. Cool cake in pan on a wire rack 20 minutes; remove from pan to wire rack, and cool completely (about 2 hours).
5. Prepare Frosting: Bring brown sugar and next 2 ingredients to a boil in a 2-qt. saucepan over medium heat, whisking constantly; boil, whisking constantly, 1 minute. Remove from heat; stir in vanilla. Gradually whisk in powdered sugar until smooth. Gently stir 3 to 5 minutes or until mixture begins to cool and thicken. Immediately pour frosting over cooled cake.