Soak raisins. In a small bowl, stir together vanilla and raisins. Let soak until ready to use.
Prep oven and pan. Preheat your oven to 450f. Line a cookie sheet with parchment paper or silicone baking mat. Or use a round cake pan (lightly grease). You can also bake in a cast iron pan.
Combine dry ingredients. In a large mixing bowl, whisk together flour, baking powder, baking soda, cinnamon and salt.
Cut in butter. Using your fingertips, two knives, or a pastry blender, cut the butter into the dry ingredients until the butter are pea-sized. You should still see visible solid pieces of butter.
Add raisins. Stir in the soaked raisins and any leftover vanilla extract.
Add buttermilk. Pour in your cold buttermilk and stir to combine. It will form a shaggy, sticky dough.
Make swirl/topping. This is going to be layered into the biscuit dough and some will be sprinkled on top. In a small bowl mix together the cinnamon and sugar. Reserve some for sprinkling on top.
Shape the biscuits. Empty the bowl onto a lightly floured surface. Pat or roll the dough into a 1/2-inch thick and sprinkle on some cinnamon sugar. Then fold the dough in half. Repeat this process 3 more times to create layers.
Cut out the biscuits. Pat the dough out into a 3/4 inch to 1-inch thick circle (I like thick biscuits so I make the dough about 1-inch thick). Using a biscuit cutter (or the rim of a large drinking glass) press straight down into the dough. You can also use a sharp knife or pizza cutter and just cut the biscuits out into squares. Do not twist the cutter, which can cause your biscuits to come out lopsided. Place biscuits on prepared baking sheet or in baking pan. Place the biscuits next to each other on the cookie sheet so they touch.
Top the biscuits. I use a pastry brush and lightly brush on the leftover buttermilk that is in my measuring cup and brush the tops of the biscuits. I then sprinkle on the remaining cinnamon sugar.
Bake the biscuits. Bake for about 15 minutes until golden brown. Remove from the oven and allow to cool on pan for about 5 minutes. Remove biscuits to continue to cool on a cooling rack.
Make icing. In a small bowl, combine the powdered sugar, milk, vanilla, and cinnamon. Adjust consistency if needed. Drizzle on biscuits once cool.