In a saucepan over medium heat, add sweetened condensed milk, 1 cup 1% milk and cocoa powder. Whisk until cocoa powder is blended. During the process just before the mixture starts to simmer, add cornstarch mixed with the remaining ½ cup 1% milk; whisk until mixture thickens, about 5 minutes.
Remove from the heat and transfer to a measuring cup. Add mini chocolate chips, vanilla extract and fleur de sel; whisk until well combined. Carefully fill up the molds, insert sticks and transfer to the freezer for at least 24 hours.
The day after, dip molds in a bowl filled with very hot water until the fudgesicles release. Yield 3 cups.