If you plan on freezing any of the pre-baked cinnamon rolls, here's what you want to do. Freeze them for an hour on a baking sheet or until they'll hold their shape, then drop them into a freezer bag, squeeze out any air and seal well. The night before you want rolls for brunch, thaw them overnight on your counter top, covered with a clean dish towel, and bake per the instructions below any time the following morning.
Start by combining the cinnamon and sugar in a small bowl. Spread half of the butter evenly over one rectangle of the dough. Sprinkle half of the sugar mixture evenly across the butter. Roll the dough up tightly lengthwise, then turn it so that the seam side is down. Cut the roll into 12 equal slices, a serrated knife works best. You can bake these, cut-side up, on a parchment lined baking sheet, in cupcake liners, or in a buttered baking dish. I used a well-buttered standard pie dish. Unless you are using individual cupcake liners, you want to arrange the slices about 1/2-inch from each other on the baking sheet or in the baking dish. They rise and expand, and end up nice and snuggly in/on the pan. Repeat with the remaining rectangle of dough and filling. You can freeze any slices you aren't going to bake at this point.
Whisk the powdered sugar with the buttermilk, salt, and vanilla together in a small bowl. Stir until smooth, let sit for a few minutes, then adjust with more sifted powdered sugar if you want a stiffer icing, more buttermilk to thin it out.If icing your cinnamon rolls, spread a bit on each individual roll before serving or serving the icing on the side with a palette knife for individual spreading.
Adapted from the Cinnamon Bun recipe in Lotta Jansdotter's Handmade Living: A Fresh Take on Scandinavian Style by Lotta Jansdotter.