Prepare the Dough:

1. In a stand mixer, combine warm water, vegan cane sugar, and instant yeast. Let sit for 5 minutes until bubbly.
2. Add pumpkin puree and vanilla extract, mixing well.
3. Gradually add 2 cups of bread flour, black cocoa powder, salt, and nutmeg. Mix until combined.
4. Add another cup of flour, then switch to the dough hook. Add remaining flour gradually while kneading for 8-10 minutes. Add vegan butter 1 tbsp at a time. The dough should be soft and slightly sticky.

Let Dough Rise:

1. Form the dough into a ball, cover the bowl, and let rise in a warm place for 30 minutes.

Prepare the Custard Filling:

1. In a saucepan, combine non-dairy milk, brown sugar, cocoa powder, and cornstarch. Cook over medium heat, stirring constantly until thickened (about 3-5 minutes).
2. Add vegan chocolate chips and vegan butter, stirring until melted. Remove from heat and stir in vanilla extract. Let cool.

Roll Out the Dough:

1. Roll out the dough on a floured surface to ½ inch thickness.
2. Cut out donuts using a 3.5-inch donut cutter. Place on a baking sheet and let rise for another 15-20 minutes.

Fry the Donuts:

1. Heat vegetable oil to 350°F (175°C).
2. Fry donuts in batches for about 1 minute on each side until golden brown. Remove and place on a cooling rack.

Coat and Fill:

1. Toss fried donuts in sugar.
2. Once cooled, use a piping bag to fill each donut with chocolate custard.