Preheat the oven to 180°C or 360°F. Line a rectangular baking dish with baking paper, we used a 17cm by 26cm tin.
Place the Medjool dates in a heatproof bowl and cover with the boiling water. Sprinkle the bicarb soda over the top and set aside for 10 minutes.
Combine the remaining wet ingredients in a mixing bowl. Whisk until smooth.
Combine the dry ingredients in another mixing bowl. Whisk to ensure there are no lumps. Pour the wet ingredients into the dry and stir.
Mash the dates until a thick paste forms. There can be some lumps of dates remaining; this will add some texture to the slice. Add the date mixture to the cake batter and stir until incorporated.
Pour into the lined baking dish. Arrange the apple slices on top and sprinkle over the flaked almonds. Bake for 30-35 minutes or until cooked through.
Once the slice is cooked, remove from the oven. Allow to cool in the tin for 10 minutes before transferring to a wire rack to cool completely.
Slice and serve with Greek yoghurt or ice cream. Any leftovers can be kept in an airtight container in the fridge for up to 4 days.
