Preheat the oven to 350 F (177 C). Line two large baking sheets with parchment paper.
In a large bowl, whisk the flour, baking powder and salt together until well combined.
2¼ cups (270 g) all purpose flour, 1½ teaspoon baking powder, ½ teaspoon salt
In a mixing bowl fitted with paddle attachment, beat the softened butter, powdered sugar and granulated sugar until light and fluffy. This takes about 3 - 4 minutes on medium speed. With the mixer on low, beat in the eggs, vanilla extract and almond extract if you are using in the cookies. ¾ cup (170 g) unsalted butter, softened, ½ cup (100 g) granulated sugar, ½ cup (60 g) powdered sugar, 2 large eggs (US), room temperature, 2 teaspoon (10 ml) vanilla extract, ¼ teaspoon almond extract
On low, mix in the dry ingredients until just combined. Stir in the rainbow sprinkles.
3 tablespoon rainbow sprinkles
Using a large cookie scoop, scoop about 3 tablespoons (45 ml) of cake batter cookie dough onto a lined baking sheet. I like to use a large cookie scoop to get perfectly portioned cookies. Bake the birthday cake cookies for 12 - 14 minutes.The edges will be set and lightly golden brown. Cool the cookies on the hot cookie sheet for 3 - 4 minutes before transferring onto the cooling rack to cool to room temperature. While the cookies cool, make the vanilla frosting. Make the vanilla buttercream frosting by beating the softened butter with powdered sugar, vanilla extract, heavy cream and salt until well combined. Scrape the sides of the bowl and increase the speed the medium speed for 3 - 4 minutes until the frosting is light and fluffy.
6 tablespoon (85 g) unsalted butter room, temperature, 2 cups (240 g) powdered sugar, 1 teaspoon (5 ml) vanilla extract, ¼ teaspoon salt, 2 tablespoon (30 ml) heavy cream
Top each cake cookie with the vanilla frosting and more sprinkles and enjoy!
¼ cup (59 ml) rainbow sprinkles