Preheat oven to 350°F (176°C) and grease the pan, SEE NOTE
In a medium mixing bowl, whisk the 3 cups flour, 1/3 cup cocoa powder, 1 ½ tsp baking powder, and ½ tsp sea salt until completely combined
In a large mixing bowl, beat the 1 ½ cups vegan butter and 2 cups of sugar on a high speed until light and fluffy. Be patient and allow the butter to develop air pockets so it gets really fluffy.
Add the 2 tsp of Nielsen-Massey Pure Peppermint Extract, 3 tsp Nielsen-Massey Madagascar Bourbon Pure Vanilla Extract, and 5 vegan eggs to the butter and sugar mixture and beat on a high speed until light and fluffy. The butter may look like it curdled at first, just keep beating, it will turn creamy and fluffy.
Once the butter and egg mixture is light and fluffy, add 1/3 of the flour mixture and beat on a low speed until it just begins to combine.
Add 1/3 of the milk and beat until just combined
Alternate with the flour and milk until all of it is just combined.
Remove the mixing bowl and finish stirring with a spatula, scraping the bottom to make sure that all of the butter is mixed into the flour.
Pour the batter into the prepared pan and bake for approximately 1 hour, or until a wooden toothpick is inserted into the center comes out clean.