In a large bowl cream together 1/2 cup butter or margarine, 1/2 cup peanut butter, white sugar, brown sugar and vanilla. Add egg and beat well.
In another bowl combine the flour, bicarb soda, baking powder and salt. Add these dry ingredients to the creamed mixture. Stir. Add oatmeal and stir.
Drop by teaspoons onto greased baking tray and press each mound down with a fork to form 5mm thick biscuits. Bake at 180 degrees C for 10 minutes, or until biscuits are a light brown.
To Make Filling: Cream 3 tablespoons butter or margarine with the icing sugar, 1/2 cup smooth peanut butter and the cream. Spread filling onto half of the cooled biscuits then top with the other half to form sandwiches.