from Elixirs of Life by Mrs C. F. Leyel
Line a dish with red rose petals, then place in it some butter wrapped in its own paper. Cover the whole with more rose petals, pressing them closely together until the dish is full. Put in a cool larder overnight. Then cut thin slices of bread and spread them with the butter, make into sandwiches, and place fresh rose petals on the top of the butter so that the edges of the petals show outside the sandwich.
So I assume the butter stays wrapped and the scent of the roses some how gets through the paper - would not work with foil wrapped butter. I suppose one could simple put some petals into the butter as well....though the very bottom end of rose petals can be a little dry/bitter. Of course petals can be used in salad; they look wonderful surrounding poached salmon. Primroses are good in salad.
It is also possible to make cake decorations with rose petals ...and primroses and pansies, any edible flower. Take an egg white, lightly whisk it then paint it onto dry petals and dip and sprinkle it in caster sugar. Allow to dry on baking parchment. They look beautiful and taste good too.