Prepare date paste by combining chopped dates, water and vinegar in a saucepan, bringing to the boil and simmering for 5 minutes or until the mixture reaches a paste-like consistency. Set aside.
Preheat oven to 170 degrees celsius (fan-forced).
Cream butter and sugar in a stand mixer.
Add egg and beat again.
Mix in milk, flour and bicarb soda, and coconut, alternating after adding about 1/3 of each.
Grease two 27 x 17cm (approx) slice tins.
Take 2/3 of the mixture and divide evenly between the two slice tins. Press mixture into the bottom of the tins.
Spread date paste as evenly as possible onto mixture in tins then sprinkle with chopped walnuts.
Divide the remaining mixture into half and roll out each half with a rolling pin. Carefully place onto the top of the date and walnut layer. Trim around edges so it fits nicely in the tin.
Pierce top layer with a fork, leaving a 4-5cm gap between piercings.
Place slice tins in oven and cook slice for 15-20 minutes or until golden on top.
When cold, combine icing sugar, rosewater and pink colouring and drizzle over slice.
Cut into squares and remove from tins. Sprinkle with dried rose petals.