Pre-heat oven to 350°F (180°C). Grease and flour an 8 inch square or 9 inch round cake pan.
In a medium bowl whisk together flour, baking powder, baking soda and salt.
In a medium bowl beat together butter, sugar and vanilla, until light and fluffy (approximately 3 minutes), add the egg and beat, add the mashed bananas and beat to combine.
To the creamed mixture alternately add the dry ingredients with the sour milk, beat on high until smooth.
Pour into prepared cake pan and bake for approximately 30-35 minutes or until a toothpick comes out clean or with a few crumbs attached. Let cool completely before frosting. Enjoy!
CREAM CHEESE FROSTING
In a medium bowl beat butter and cream cheese until creamy approximately one minute. Add icing sugar a little at a time, continue beating, add the cream beat approximately 3 minutes until fluffy. Depending how you like your frosting, if too thin add more powdered sugar, if too thick add a drop of cream.
Notes
To make homemade pastry/cake flour, for every cup of all purpose flour remove 2 tablespoons and substitute with cornstarch. Sift them together to remove any lumps. You could also make 12 standard size cupcakes, although they will take a shorter amount of time to bake, approximately 18-20 minutes.
The baked cake will keep a day or two in an airtight container at room temperature or one week in the fridge. Bring it to room temperature before serving. If the cake is frosted then it definitely should be refrigerated.
Carefully wrap the unfrosted completely cooled cake in a double layer of plastic wrap and then place in a freezer bag, it will keep up to 3 months in the freezer.