Sift together the flour, cinnamon, baking soda and a pinch of salt.
With electric beaters, beat the butter and sugars on high speed in a large bowl until mixture is fluffy and pale, about 4 minutes. Add the egg and vanilla essence; beat until well combined. Stir in the flour mixture with a wooden spoon; add the sour cream and pecans.
Tear off 50-cm sheet of cling wrap and sprinkle lightly with flour. Transfer dough to cling wrap and shape into a log 38 cm in length. Roll the log tightly in the cling wrap and refrigerate until firm, about 2 hours. (Alternatively, wrap the dough in heavy-duty aluminium foil and freeze for up to 1 month.)
Preheat oven to 190°C. Slice the dough into rounds about 3 mm thick to make 72 biscuits. Place 1 cm apart on ungreased baking trays.
Bake until crisp and golden brown around the edges, about 8 minutes, taking care not to overbake. (If you're using frozen dough, increase the baking time to 10 minutes.) Transfer the biscuits to wire racks to cool completely. Store in airtight containers.