To make it I cut a two rounds of brown felt about 2.5 inches in diameter, and then I cut a piece of white felt to mimic the frosting and sewed that to one of the brown circles. Then I sewed the sequins onto the white felt, being sure to cover the whole area. The sequins I used were very pale purple with what I think is called an Aurora Borealis (AB) finish, which gives a greenish hue to the reflected light and I used invisible thread. A little bit of wadding was sandwiched between the front and back to give it some body, and the whole lat was simply sewn together with a whip stitch. Two holly leaves cut from metallic card and flatback rhinestone berries finished the brooch off.
The sewing of the sequins took a while, but it was a labour of love. If you didn't have the time or inclination then I suppose a clear-drying fabric glue would also work, but I love the meditative quality of hand-sewing. I will be sporting my pudding brooch this year, and I might even make up a few more to hang around the house.