Butter or spray 15 regular muffin tins or line with paper cups.
For the beetroot puree
Boil, steam, or microwave unpeeled beetroot until tender. Peel beetroot while warm and process until smooth. You need 200ml of puree (about 3/4 cup, a little more).
For the muffin:
Beat oil with sugar in a large bowl. Add beetroot puree and mix well. Add eggs one by one, beating until fully incorporated, and vanilla.
Add gluten-free all-purpose flour, cocoa powder, baking powder, and salt along with the buttermilk. Add 3/4 of the chocolate chips and mix.
Fill the muffin cups ¾ full, dividing the mixture as evenly as possible. Top with the remaining chocolate chips.
Bake for 25 minutes or until a toothpick inserted into the center comes out clean
Let cool before removing.
Notes
Store the muffins in an air-tight container at room temperature for 3 days or in the refrigerator for up to 5 days.