Heat oven to 350° F. Toast the coconut on a baking sheet, tossing occasionally, until golden, 10 to 12 minutes. Butter two 8-inch round cake pans. In a large bowl, whisk the flour, baking powder, and salt.
Using an electric mixer, beat the butter and granulated sugar until fluffy. Beat in the eggs one at a time, then the vanilla and 3/4 cup of the preserves. Alternately add the flour mixture and the milk, mixing just until incorporated.
Divide the batter between the pans and bake until a toothpick inserted in the centers comes out clean, 40 to 45 minutes. Remove the cakes from the pans and let cool completely on a rack.
Using an electric mixer, beat the heavy cream, sour cream, and confectioners' sugar to form stiff peaks. Sandwich the cakes with the remaining 1/2 cup of preserves. Frost with the cream mixture and press the coconut onto the sides.
Make-Ahead Tip: Make the cakes, wrap tightly, and store at room temperature for up to 2 days. Make the frosting and frost the cakes up to 4 hours before serving. Refrigerate until 30 minutes before serving.