Place a stick of butter (½ cup) in the freezer for 20-30 minutes.
In a large bowl, whisk together the flour, brown sugar, baking powder, cinnamon, ginger, cloves, nutmeg and salt.
Remove butter from freezer and grate into flour using a box grater. Toss the butter into the flour using your fingertips.
In a small bowl, whisk together the pumpkin, egg, vanilla, sourdough starter and ¼ cup heavy cream. Pour over flour mixture and, using a spatula, gently work the mixture together into a shaggy dough.
Turn dough out onto a lightly floured counter and gently knead until the dough comes just together. (Do not knead past this point as over-worked dough will yield tough scones. You just want it to come together and be able to hold its shape.)
Press the dough into a one-inch thick circle and cut into eight equal triangles.
Place scones onto a parchment lined baking sheet and set in the fridge while the oven preheats.
Preheat oven to 400°F. Bake for 20-25 minutes or until edges are lightly browned. Remove from oven and allow to cool on rack.
To make glaze, combine one cup powdered sugar with two tablespoons of maple syrup, ½ teaspoon of cinnamon, a pinch of salt and one or two tablespoons of milk or cream until you have a good consistency to drizzle over your scones.