1) Mix the oats, flour, sugar and bicarbonate together and then stir in the butter.
2) Press half this mixture into the base of a 30 cm x 17 cm x 2 cm tin. Spread the mincemeat over this and then carefully scatter the remaining mixture over the top.
3) Bake in a pre-heated oven 180 degrees C/gas 4 for 25-30 minutes or until golden brown. Allow to cool before slicing into bars. Store in an air-tight container.