Preheat the oven to 350ºF (180ºC). Line an 8-inch square baking pan with parchment paper, leaving a couple of inches of overhang.

In a medium-size bowl, whisk together the flour, cornstarch and salt.

In a large bowl, beat the butter, sugar and orange zest until light and fluffy. Beat in the egg until incorporated, then beat in the extracts. Beat in the food coloring a little at a time, if using. Beat in the flour mixture just until combined. Do not over mix.

Spread the batter evenly into the prepared pan. Smooth the top with a spatula. Bake until the top is set and the edges start to turn light golden brown, about 18-20 minutes. Let cool in the pan. Once cooled, remove the bars from the pan using the parchment paper as handles. Frost and cut into 2-inch squares. Add candy decorations or sprinkles if desired. Frosting

In a medium-size bowl, beat the butter and cream cheese together just until smooth and combined. Add the powdered sugar, vanilla bean paste, salt and 1 teaspoon of milk. Beat until smooth. Mix in additional milk a little at a time, if needed, to reach the desired consistency. Stir slowly with a spatula to remove any bubbles.