To a saucepan, add 3 tbsp (1 ½ oz) water. Sprinkle gelatin into saucepan and stir with a fork to incorporate with water (the gelatin will be lumpy). Allow gelatin to bloom in water for 5 minutes. After gelatin has bloomed, pour remaining 3 tbsp (1 ½ oz) water into saucepan and turn stovetop heat to medium to simmer until mixture is free from any lumps of gelatin, whisking frequently. Remove saucepan from stove top burner and set aside.

In a food processor, pulse monk fruit sweetener until powdered.

In a mixing bowl, whisk together powdered monk fruit sweetener, cream of tartar, and salt. In a separate mixing bowl, using an electric mixer set to high speed, beat egg whites until stiff peaks form. Slowly, in small batches with electric mixer at lowest speed, add in dry ingredient mixture. Turn electric mixer off and pour in vanilla extract. Turn electric mixer back on to highest speed and continue to mix egg white mixture for 1-2 minutes.

Very slowly, with electric mixer turned to lowest speed, pour steady stream of gelatin mixture into egg white mixture. Once all of gelatin mixture has been poured in, increase speed of electric mixer to highest speed and mix until mixture becomes creamy.

In a saucepan over medium heat, melt butter. Pour marshmallow mixture into saucepan of melted butter and stir with a rubber spatula until mixture is melted and fluffy. Remove saucepan from heat and transfer mixture to silicone mold cavities. Transfer fat bombs to freezer to chill for 20 minutes before popping fat bombs out of silicone mold cavities.