Preheat the oven to 180°C (160°C fan forced). Grease and base-line 2 x 16cm round cake pans with baking paper.
Open the cake box, remove enclosed frosting sachet and reserve for another use. Stir the brownie mix, butter and eggs in a medium bowl with a wooden spoon until combined.
Divide the cake batter evenly between the 2 cake tins.
Bake in the centre of the oven for around 20-25 minutes or until a rounded knife, inserted 5cm from the edge of the pan comes out almost clean. Leave in the pans for 5 minutes then turn out onto a wire rack and leave to cool completely.
Place the frosting in a small bowl and beat in enough pink gel food colour to give an even pink colour. Peel off the baking paper lining from the cakes and place one on a serving plate. Spread over half of the frosting then place the second cake on top. Spread the remaining frosting on the top cake and swirl with the tip of the palette knife.
To make the marshmallow ‘petals’, cut each marshmallow in half diagonally with small scissors. Place the sprinkles on a flat plate and dip the cut side of each marshmallow half into the sprinkles.
Place 3 chocolate chips in the middle of the cake, spaced in a triangle, then place 6 of the marshmallow ‘petals’, cut side up, around each chocolate chip to create 3 flowers. Repeat with the rest of the chocolate chips and ‘petals’ to create 6 more flowers around the edge of the cake.