In a large wide-mouth jar, pour in the vodka and set aside.

In a saucepan over medium heat, melt the butter until it starts to foam, then allow to cook until the butter starts to turn golden. Remove from heat and allow to cool to room temperature.

Pour the cooled brown butter into the vodka, do not stir. Seal and allow to mellow and infuse the vodka for at least an hour. Place in the freezer to solidify overnight or up to a week.

Remove from the freezer and carefully remove the solid butter with a knife. Save the butter in a ziplock bag in the refrigerator to use in other recipes.

Preheat the oven to 400°F. Line a baking sheet with parchment paper.

In a bowl, add the diced butternut squash, maple syrup, cinnamon, and nutmeg, tossing to coat.

Transfer butternut squash to the baking sheet and spread out in a single layer.

Roast in the oven for 10 - 15 minutes.

While the butternut squash is roasting, place the sugar and water in a saucepan over medium heat, and bring just to a boil, stirring occasionally, and cooking until the sugar has dissolved. Remove from heat.

Once the butternut squash has roasted, remove it from the oven and carefully add to the simple syrup. Cover and allow to infuse for 1 - 2 hours. Remove the squash with a slotted spoon and transfer the flavored simple syrup to a jar and keep sealed in the refrigerator until ready to use (up to 2 weeks).

In a shaker filled with ice, add the brown butter washed vodka, spiced rum, lemon juice, butternut simple syrup, and orange bitters. Shake to well to chill.

Pour the cocktail in a glass with ice, garnish with mini marshmallows on a cocktail stick, lightly toasted if desired, and serve.