Preheat oven to 350 degrees. Prepare an 8 x 8 square pan or bundt pan with non-stick spray and gluten free flour.
Combine all cake ingredients into a mixer and mix thoroughly, making sure you scrape down the sides and bottom of the bowl to incorporate all the flour.
Pour into pan and place into oven. Bake at 350 for 40-50 minutes, until cake springs back when lightly pressed with your finger and there are no soft spots.
Prepare frosting by melting margarine and brown sugar and whisking together in a saucepan over medium heat. Add milk and vanilla, then bring to a boil while whisking. Remove from heat immediately and add 1.5 cups of the sugar while whisking.
Add up to 1/2 cup more sugar as needed to thicken the frosting. Add more almond milk or dairy substitute to thin the mixture if it gets too thick. As it cools, it will thicken further. Pour/Ladle over your completely cooled cake while frosting is warm.
Store the cake in an airtight container at room temperature. Do not refrigerate. Consume within 3-4 days.