In a stand mixer fitted with a paddle attachment, cream the butter and both sugars at medium speed until smooth, about 3 minutes. Add the salt, baking soda, and cinnamon and mix until well combined, 1 minute. Add the egg and mix for another minute. Add the flour and oats and mix on low speed until combined. Finally, add the dates in two additions to make sure they’re distributed evenly throughout. The dough will be very soft at this point.
Place two racks in the middle positions and preheat the oven to 350ºF. Line two baking sheets with parchment paper.
Using a cookie scoop, drop cookies on the prepared baking sheets, at least 3 inches apart to prevent the cookies from touching as they spread when they bake. Bake for 10 minutes, rotate the baking sheets and switch their positions in the oven, and bake for another 6 to 8 minutes, until the edges are brown and the middle is golden. Rotating and switching the sheets halfway through the baking process will ensure that the cookies bake evenly.
Let the cookies cool completely on the baking sheets. The cookies keep well for a couple of days stored in an airtight container.