Preheat your oven to 325 degrees Fahrenheit and prepare a large nonstick baking sheet with parchment paper.: The kitchen will fill with a faint warm, neutral smell as the oven comes up to temperature, and the parchment creates an even surface so cookies bake without sticking. This low heat helps cookies bake through without over browning. If your oven runs hot, they can burn on the edges, so check a minute or two early.
Use a knife to cut the cookie roll into 15 1/2-inch slices. Place the cookie dough on the prepared baking sheet 2 – 3 inches apart.: As you slice, the dough should give a soft, slightly tacky feel, and you should see even round discs. Spacing is important so cookies have room to spread and keep their round shape. A common slip is cutting uneven slices, which leads to uneven baking and odd shapes.
Bake for 10 – 12 minutes or until just becoming brown. Remove from the oven and allow to cool on a cooling rack.: While baking you will notice the aroma of baked sugar and butter growing stronger and the tops changing from pale to a hint of golden brown. Pull them when edges set but centers are still soft, because they firm as they cool. Overbaking dries them out, so watch the color closely.
Cut each of the 15 large marshmallows in half to form the bunny feet. Set aside.: Cutting marshmallows releases a sweet, faint scent, and the exposed interior looks pillowy. Use a sharp knife and press straight down to keep halves even. A slippery surface makes cutting tricky, so hold the marshmallow steady to avoid ragged halves.
Once the baked cookies are completely cool, spread white vanilla frosting over the cooled cookies.: The frosting should be thick and creamy, gliding onto the cookie with a soft, spreadable sound. Cool cookies are essential so the frosting does not melt and slide off, leaving a glossy mess. If you spread too vigorously you can tear the cookie surface, so go gently.
Sprinkle the white icing with white sparkling sugar. Then place 2 large marshmallow halves on the frosted cookies as the bunny feet.: The sparkling sugar adds a faint crunch under your teeth and catches light, making each cookie sparkle. When setting the marshmallow halves, press lightly so they adhere to the frosting without sinking. Do not press too hard or you will flatten the marshmallow texture.
Then place a mini marshmallow in the center of the cookie, just above the feet, to form the bunny tail.: The mini will sit like a little white pom pom, adding a soft touch of dimension. It should rest against the frosting and remain centered above the feet. If placed while frosting is still wet, it may slide off center, so ensure the base has some set.
Place the pink icing in a piping bag and pipe a small heel pad and toe pads on the marshmallow halves that form the feet.: Piping produces a gentle, precise sound as the frosting emerges, and the bright pink contrast defines the bunny foot pads beautifully. Use light, steady pressure and a small round tip for neat pads. Pressing too hard will create blobby pads that lose the cute detail.