Heat oven to 350 degrees. Generously grease bundt pan with butter. I use a dark non-stick pan, so that baking directions are for that type of pan. Adjust your baking time as needed.
In a large bowl, add sugar, flour, cacao powder, xanthan gum, baking powder, baking soda, sea salt, and chia seeds. Stir well.
Add boiling water, milk, and eggs. Mix well with a hand mixer.
Pour into prepared bundt pan and bake for 50 minutes or until toothpick comes out clean.
Let cool in pan for 10 minutes. Then using a small silicone spatula, loosen the sides and middle of the cake from the bundt pan. Using a cooling rack on top of the bundt pan, flip the cake upside down onto the cooling rack. Let cool completely.
Make the frosting by melting the butter in a small sauce pan. Add the cacao powder and stir well. Slowly add the powdered sugar and milk, whisking well after each addition. When all the powdered sugar and milk have been added, add the vanilla and stir. Then Frost the cake.
Carefully slice cake in half. Take the top half off VERY gently and place to the side. Gently frost the middle of the cake-remember gluten free cakes can be a little crumbly especially if the cake is warm, so make sure it is cooled. Then place the top of the cake back on and frost the outside of the cake.
I love to serve this with homemade vanilla ice cream. So delicious!