In a medium saucepan over medium-low heat, combine the melted butter and mini marshmallows. Stir continuously until smooth and fully melted, about 5–7 minutes.

In a stand mixer or large mixing bowl, add the sugar, eggs, vanilla extract, and salt. Mix on medium speed for 2–3 minutes. Gradually pour in the warm butter and marshmallow mixture, mixing until smooth.

With the mixer on low speed, slowly add the flour and coconut flakes to the wet mixture. Mix until just combined; the dough should be thick and slightly sticky.

Preheat your oven to 325°F (160°C). Line a 13 x 9 x 1-inch baking pan with parchment paper. Spread the dough evenly in the pan and bake for 20–25 minutes until set and lightly golden brown.

Once baked, cool the bars in the pan for about 30 minutes. Cut into squares and enjoy!