Stir together the flour, baking powder and salt in a small bowl. Mix together 1/2 teaspoon vanilla, 1 stick of butter and the eggs in a large bowl using an electric hand mixer. Add the flour mixture and buttermilk together. Do not over-mix or the cake may not rise.
Pour the cake batter into the cake pan and bake until a wooden pick inserted in the center comes out clean, 35 to 40 minutes. Let the cake cool in the pan for 10 minutes, and then invert onto a wire rack and cool completely.
While the cake is baking, combine the pineapple, brown sugar and remaining butter in a medium skillet and cook over medium heat. Cook until it is a syrup consistency, 3 to 4 minutes. Slice the cooled cake into 1-inch pieces. Beat together the heavy cream and remaining vanilla in a small bowl with an electric mixer until stiff peaks form, 3 to 4 minutes.
To assemble the parfaits, place 4 to 5 pieces of cake in each of 8 glasses. Top with 1 heaping tablespoon pineapple sauce, and then repeat one more layer. Then top each with 2 tablespoons whipped cream, 1 tablespoon chopped pecans and 1 cherry.