Measure out buttermilk and leave if fridge until ready to use. Keep cut butter in fridge until ready to use. Preheat oven to 400℉. Line baking sheet with parchment paper and set aside.
In a small sauté pan, add 2 tsp of cooking oil. Once warm, add sliced leeks. Cook until leeks have softened and are aromatic. Set aside.
In a large bowl, whisk together flour, sugar, baking powder, and salt. Cut in chilled butter using a pastry blender (or your hands or two forks) until flour mixture resembles crumbly, coarse sand.
Add shredded cheese and cooked leeks. Toss to combine.
Pour in cold buttermilk. Using a large sturdy spatula, fold together until dough forms.
Turn dough onto a lightly floured surface and knead together to form a ball. Roll or pat out to ¾-inch thickness.
Cut biscuits using a 2-inch cutter dipped in flour. Arrange biscuits on prepared baking sheet. Gather remaining dough and roll out again.
Bake for 15-18 minutes until bottom of biscuit is a nice golden brown. Transfer to wire rack and let cool slightly. Serve warm.