Preheat the oven to 325°F, and grease and flour ⅛" tube or bundt pan.
Blend the wet ingredients til smooth.
In another bowl, whisk the dry ingredients together.
Add the wet mix and whisk in just until blended.
Scrape batter into prepared pan.
Bake cupcakes for 20 to 25 minutes; cake 45 minutes, or until a toothpick inserted in the center comes out clean.
Remove cake from pan carefully, and let cool on rack.
Icing
Whisk non-dairy milk into flour and agar in a small saucepan until smooth. You can use a hand immersion blender if you wish, or even run it through the blender.
Heat and stir the agar mixture until it boils and thickens.
MICROWAVE OPTION: Whisk the flour, agar and milk in a microwave-proof bowl. Microwave for 45 seconds, whisk, and repeat twice, or until thick.
Let mixture cool completely. You can place it in a small bowl inside of a larger bowl of cold water to speed up the process. While cooling, the mixture will get quite stiff—don't worry!
With an electric mixer, beat butter, sugar, vanilla, and salt for several minutes until light and fluffy.
Beat in the cooled flour paste (and optional cocoa, if using) with the electric beaters and mix until smooth and fluffy.
Chill icing thoroughly before using to frost the cake.
Keep the frosted cake or cupcakes refrigerated until serving time.