Preheat oven to 350°F, grease and line a 9×5 loaf pan
Add flour, sugar, baking soda, pumpkin pie spice, and baking soda to a large bowl and whisk together.
In a separate bowl, whisk pumpkin puree, oil, and eggs together until fully combined.
Add the dry ingredients to the wet ingredients and mix until just combined. Don't overmix.
Melt butter in a small pan over low heat.
Stir in 3/4 cup marshmallows and whisk until smooth and fully melted
Let cool 1–2 minutes so it thickens slightly but is still pourable.
Pour the pumpkin batter into the prepared pan
Using a spoon, drizzled the melted marshmallow over the batter.
Add the remaining pumpkin batter over top of the marshmallow
Use a knife or skewer to gently swirl the melted marshmallow through the batter without mixing it completely.
Place in the preheated oven for 55–65 minutes or until a toothpick comes out clean in the center. If the browning is too fast, tent with foil for the last 10–15 minutes. Let cool for 15–20 minutes on a wire rack
Make the second batch of marshmallow drizzle by melting butter in a small saucepan. Then add 3/4 cup marshmallows, cream or milk, and salt, and stir together until smooth. Remove from heat and allow to cool for 2-3 minutes or until it slightly thickens, then drizzle over the top of the bread.