1. Preheat oven to 350°. Sift together first 4 ingredients. Whisk together eggs and next 3 ingredients in a large bowl. Whisk flour mixture into egg mixture.
2. Pour batter into a lightly greased 9-inch round cake pan. Dollop preserves by teaspoonfuls over batter, and gently swirl with a knife. Top with diced fruit and chopped nuts. Sprinkle with 1 tsp. granulated sugar.
3. Bake at 350° for 38 to 45 minutes or until golden brown. Cool in pan on a wire rack 5 minutes. Remove from pan to wire rack, and cool 5 minutes.
4. Whisk together powdered sugar and 2 1/2 Tbsp. buttermilk. Drizzle over warm coffee cake.