Whisk together the flour, brown sugar, cinnamon, salt, baking powder, and baking soda in a mixing bowl.
In a large mixing bowl, whisk together milk, oil, and eggs until eggs are beaten.
Add the flour mixture to the egg mixture, stirring to incorporate as you go.
Prepare a 5 to 7 quart slow cooker by lightly greasing, lining with parchment paper, or a slow cooker liner. Pour in batter.
Cover with either a clean dish towel or paper towels before putting on the lid (to prevent condensation from dripping onto the cake) and cook on high for 1 hour.