Heat oven to 325°F. Grease 3 (8-inch) round pans with shortening; lightly flour. In large bowl, beat 1 1/2 cups butter, 1 1/2 cups brown sugar and 1 cup granulated sugar with electric mixer on medium speed until well blended, scraping bowl frequently. Add milk, 1 teaspoon vanilla and eggs. Beat on medium speed 3 minutes, scraping bowl occasionally. Beat in remaining cake ingredients until mixture is smooth and well blended. (Batter will be thick.) Spread about 2 1/2 cups batter in each pan.