Preheat your oven to 350°F (175°C). Place parchment paper in an 8x8-inch or 9x9-inch baking pan.
In a large bowl, combine the flour, baking powder, and sugar by whisking them together. Set aside.
In a separate bowl, cream the vegan butter and granulated sugar until light and fluffy. Add the almond milk and vanilla extract, and mix until fully combined.
Slowly mix the dry ingredients into the wet mixture, stirring until a soft dough comes together. Spread the dough evenly across the bottom of the prepared baking pan.
Use a spatula to smooth the surface. Bake for 20-25 minutes, or until the edges are lightly browned.
Remove the pan from the oven and let the cookie bars cool completely in the pan before frosting them.
In a medium bowl, whip the vegan butter and powdered sugar together until smooth. Add almond milk, one tablespoon at a time, until the frosting reaches a spreadable consistency.
Smoothly spread the frosting over the cooled cookie bars. Add sprinkles or any toppings you like.
After the frosting has set, cut the bars into squares or rectangles. Serve and enjoy!