In a large bowl, sift flour, cornstarch, cocoa powder, powdered sugar, baking powder, baking soda, instant coffee, salt and whisk to combine. Add in oat milk, vanilla, coconut oil, white vinegar. And until well combined.
Make the buttercream.
Whip butter I n the stand mixer bowl with the paddle attachment, on medium to high speed for about 2 minutes. Stop mixer and add the sifted powdered sugar. Mix on low speed until incorporated , scrape the bottom and sides of the bowl and then add in 1 tbsp of coconut cream (if you’re looking for thinner consistency, add more coconut cream) mix on high speed for 2-3 minutes until smooth.
Pipe the frosting onto the cooled cupcakes and serve. Enjoy!