Place unopened can of sweetened condensed milk on its side in a slow cooker. Add enough water to cover can by ~2”.

Cook on LOW temperature for 8 hours.

Remove can from water and let cool before opening. (Note: To cool the can quickly, submerge it in cold water for 10 minutes.)

Open can and transfer Dulce de Leche into a bowl for dipping. (see note)

Using a large bowl, combine flour, sugar, baking powder and salt.

Cut the butter into ½” cubes. Using a pastry cutter (or two table knives), cut the butter into the dry ingredients until the mixture resembles coarse crumbs.

Add milk and stir until well combined.

Turn dough out onto a well-floured work surface. Knead for 1-2 minutes or until dough comes together into a ball. (Note: If needed, add another 1-2 Tbsp of flour at this stage.)

Using a large Dutch oven or a deep fryer, add enough vegetable oil to fill bottom 3” of the pot. Heat oil to 350°F.

Pinch off ~1½ Tbsp of dough and gently roll into a ball; set ball aside. Repeat process until all dough has been rolled into balls.

Before you start frying the donut holes, combine the sugar and cinnamon (for rolling) in a shallow bowl; set bowl aside.

Drop several dough balls into oil. Fry, flipping occasionally, until golden brown (~2-3 minutes total). Transfer donut holes to a paper-towel or brown paper bag lined plate to drain. Repeat process with remaining dough balls.

While donut holes are still warm, roll in the cinnamon-sugar mixture.