Frosted sugar cookie bars

Mix the flour, baking powder, baking soda, cornstarch and salt together in a medium bowl; set aside.

Cream the softened unsalted butter with the sugar at medium-high speed for about three minutes until light, creamy and fluffy; scrape down the sides and mix a few seconds more.

Add the egg, an extra egg yolk, the vanilla and the optional almond extract; mix.

Add the dry ingredients and mix to a thick cookie dough; scrape down the sides.

Mix in the rainbow sprinkles (optional). No chilling is needed.

Spread the thick dough into a nine inch square pan lined with parchment, scraping it gently out to the sides.

Bake at 350F for 25 to 26 minutes, checking at 25, until the edges are lightly browned and the centre still looks a little soft.

Cool the bars completely in the pan before frosting.

For the vanilla buttercream, beat the base for two minutes until smooth; scrape down the sides.

Add confectioners' sugar, room-temperature heavy cream and vanilla extract; beat, taste, and add a pinch of salt; beat three full minutes until fluffy, scraping once.

Optional: tint pink with a small drop of red gel food coloring added on a toothpick.

Variation: freeze-dried strawberry powder for a strawberry frosting, or freeze-dried blueberries for blueberry.

Lift the cooled bars out by the parchment and spread a thick layer of frosting over them with an offset spatula.

Top with non-pareils and pastel confetti sprinkles; cut.