Preheat the oven to 350°F. Prepare a standard sized cupcake/muffin baking tray with paper cupcake liners.
Sift the flour, sugar, cinnamon, baking powder, baking soda and salt in a large bowl. Whisk to blend thoroughly.
In a medium sized bowl, whisk together the mashed bananas, plant-based milk, oil, vinegar and vanilla extract.
Pour the liquid ingredients into the dry, and mix with a spoon just until combined. Do not over mix.
With a medium scoop or large spoon, fill the paper liners about 2/3 full with the cupcake batter. Bake for 18-22 minutes, or until a toothpick inserted comes out clean or with a few cooked crumbs. Cool the bases in the tray for 5-10 minutes, then gently transfer each cupcake to a cooling rack. Let cupcakes cool completely before frosting or the frosting will melt.
For the Cinnamon Ermine Frosting:
Whisk the flour and cinnamon together in a small bowl. Pour in the cold milk slowly, whisking constantly. Pour through a fine mesh sieve into a small pot and place over medium-low heat, stirring constantly. Add the brown sugar. Once the mixture thickens and is bubbling, cook another 2 minutes stirring constantly. Do not under-cook or the frosting will taste like flour and will not thicken enough.
Pour into a bowl and place plastic wrap directly over the surface to prevent a skin from forming. Let cool completely to room temperature.
In a stand-mixer with whisk attachment, beat the vegan butter on high for 5 minutes, scraping down the sides as necessary. Beat in the vanilla extract. Reduce the speed to medium, and add the cooled flour mixture a spoonful at a time. Once it's all added, beat on high for about 5 minutes or until light, fluffy and silky.
Pipe the frosting onto completely cooled cupcakes.
Make Ahead: The flour mixture for the frosting can be prepared ahead of time. Store in the fridge, and bring to room temperature before making the frosting.Tips for the Frosting: If curdling happens, your frosting is too cold. Place the bowl over steaming hot water until the vegan butter just starts to melt. Try whipping again.If your frosting is too soft and slouching, it is too warm either from handling or the kitchen being hot. Place the bowl in the fridge for 10-15 minutes at a time until it firms up.This frosting can be piped but will not hold up in hot temperatures as the vegan butter will melt causing the entire frosting to soften.