• Preheat oven to 350°F. Combine sour cream and milk. Set aside.

Cream butter and sugar:

• Beat butter at medium speed with an electric mixer until creamy. Gradually add sugar, beating well. Add eggs, one at a time, beating until well after each addition.

Finish batter, add to pans:

• Combine flour, baking powder, and salt; add to butter mixture alternately with sour cream mixture, beginning and ending with flour mixture. Beat at medium-low speed until blended after each addition. Stir in vanilla and rum extract. Pour batter into 2 greased and floured 9-inch round cake pans.

Bake cake layers:

• Bake at 350°F for 30 to 35 minutes or until a wooden pick inserted in center comes out clean. Cool in pans on wire racks 10 minutes. Remove from pans to wire racks, and let cool 2 hours or until completely cool.

prep Caramel Frosting

• Melt small amount of sugar:

  Sprinkle 1/3 cup sugar in a heavy, 3 1/2-qt. Dutch oven; cook over medium heat, stirring occasionally, 3 minutes or until sugar is melted and syrup is a very light golden brown. Remove from heat.

  Stir together 1 Tbsp. flour and 2 1/2 cups sugar in a large saucepan; add milk, and bring to a boil over medium-high heat, stirring constantly. Remove from heat.

  Set Dutch oven with caramel over low heat until sugar is liquefied if cooled. Stir until smooth.

  Gradually pour about one-fourth hot milk mixture into caramelized sugar, stirring constantly until smooth. Take care: the mixture will bubble and sputter as the liquid is absorbed into the caramel. Gradually stir in remaining hot milk mixture until smooth.

  Cover, and cook over low heat 2 minutes. Increase heat to medium; uncover and cook, without stirring, until a candy thermometer reaches 238°F (soft-ball stage, about 10 minutes). Add butter, stirring until blended. Remove from heat and let stand, without stirring, until temperature drops to 110°F (about 1 hour).

  Pour caramel into bowl of heavy-duty electric stand mixer. Add vanilla, and beat at medium speed (setting 4) with whisk attachment until spreading consistency (about 20 minutes).

  Boil sugar and milk:Warm up caramel:Add hot milk mixture to caramelized sugar:Cook caramel frosting:Mix frosting in stand mixer:

Frost cake layers:

• Spread Caramel Frosting between layers and on top and sides of cake.