Peel, core and slice apples. Spinkle with lemon juice to prevent browning.
Melt butter in multi cooker on 'Warm' setting (then you won't need to grease it later). Pour melted butter into mixing bowl; add sugar and vanilla. Add eggs, one at a time, mixing well every time. Add soured cream; mix well.
Combine flour, salt and bicarbonate of soda in a separate bowl; gently stir into cake mixture.
Arrange 1/3 of apple slices on the bottom of multi-cooker pot. The bottom and sides of the pot should be greased from melted butter. You may melt additional butter if needed.
Fold the remaining 2/3 of apples into the cake mixture. Pour or spoon cake batter into multi cooker, on top of apple layer. Close lid. Set for 1 hour on 'Bake' setting. After signal, let stand for additional 15-20 minutes on 'Warm' setting.
Cover multi cooker pot with serving plate and turn cake over, out onto the plate. Sprinkle with caster sugar, if you like.