Preheat your oven to 350 degrees. Spread the flour on a rimmed baking sheet and bake for 5 minutes.
While the flour is baking, in the bowl of a large stand mixer, cream the butter and the sugar until light and fluffy, about 3 to 6 minutes. Beat in the vanilla.
Whisk salt into the toasted flour. Then add the flour mixture to the mixer. Beat just long enough for the flour to be somewhat combined. Then turn the mixer on high and beat until just combned. Scrape down the sides as necessary.
With the mixer still running, add in the sweetened condensed milk. You may need to stop the mixer periodically to scrape down the sides.
Enjoy immediately or store in the refrigerator for 4 to 5 days.