Preheat your oven to 325°F. Generously grease a half sheet pan (approximately 18"x13") using butter or baking spray, and set it aside.

In a separate medium bowl, mix together the all-purpose flour, baking powder, and kosher salt, then set this dry mixture aside.

Using a stand or hand mixer, beat the softened butter with the granulated sugar until the mixture becomes light and fluffy, around 3 to 4 minutes. Incorporate the eggs and almond extract, mixing until fully integrated. Gradually add the flour mixture into the wet ingredients, blending thoroughly until a cohesive dough forms.

Evenly press the dough into the prepared baking pan, smoothing the surface with your hands or a pastry roller.

Brush the top of the dough with milk using a pastry brush (you may not require the full amount). Sprinkle the sliced almonds over the surface, gently pressing them into the dough to adhere.

Bake in the preheated oven for 20 to 22 minutes, ensuring the bars remain pale and do not brown.

Allow the bars to cool in the pan for about 5 minutes before slicing them into individual portions. If the texture is too soft for cutting, let them cool slightly longer. Transfer the cut bars to a wire rack to cool completely.

Once the bars have cooled, prepare the glaze by whisking together the powdered sugar, almond extract, and milk until smooth. Drizzle the glaze over the bars and let it set before serving.