Measure the brown sugar, baking soda, salt, vanilla and egg into a mixing bowl. Add the buttermilk. Add the flour. Stir until thoroughly combined.
Turn dough out onto a lightly floured surface and knead for a minute or two. Roll the dough into a 12-inch by 24-inch rectangle. Using a rubber spatula, spread with butter. Sprinkle with sugar and cinnamon.
Roll the dough into a log and stretch slightly. Cut into two-inch pieces and put the pieces into greased muffin tins or muffin tins lined with cupcake papers.
Bake for 15 minutes, or until golden brown. Allow the muffins to cool for 5 minutes, and then remove from the muffin tins.
Drizzle with icing (if using) when cool.
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