Preheat oven to 350-degrees F. Line a 9- x 13-inch baking pan with heavy aluminum foil. Butter the foil and set baking pan aside.

In a medium mixing bowl, whisk together the flour, baking powder and salt. Set aside.

Using a stand mixer or hand-held electric mixer, beat together the butter and powdered sugar until creamy, about 1 minute.

In a small bowl, lightly whisk together the egg yolk and the whole egg. Add the eggs and the vanilla extract to the butter and powdered sugar mixture. Beat until well blended and smooth.

Blend in the flour, a little at a time, until well incorporated. Transfer dough to the prepared baking pan. Using your hands, push dough evenly over the bottom of the pan.

Bake for 16-18 minutes or until cookie crust is medium golden brown. Remove from oven and allow to cool completely in the pan. Putting the partially cooled pan in the refrigerator can help quicken the cooling process.

In a 3 quart sauce pot, melt the butter over medium heat. Add the white and brown sugars. Continue to cook over medium heat, stirring or whisking constantly until mixture is smooth.

Add the corn syrup or golden syrup and whisk together. Add the sweetened condensed milk, stir well. Using a pastry brush dipped in water, brush the sugar from the edges of the pot. This is necessary to keep sugar crystals from being reintroduced to the caramel. If sugar crystals are reintroduced to the caramel after it has been cooked to the desired stage, it will cause the caramel to crystallize and become grainy.

Cook, stirring constantly, over medium or medium low heat until caramel is hot and bubbly and reaches a soft ball stage, about 240-245 degrees F on a candy thermometer. Stir in vanilla.

Pour caramel over cooled cookie crust. Cool completely before proceeding. Again, the cooling process can be aided by placing the partially cooled pan in the refrigerator. When ready to proceed with coating the cookie bars, using the overlapping foil as handles, gently lift the caramel coated cookie slab and place on a cutting board. Carefully pull the foil away from the sides of the caramel and crust. (Leave foil in place under the crust.)

With a sharp knife, cut into bars measuring approximately 3" x 1/2-5/8". There should be 69-78 bars. You may want to use a ruler to help make consistent cutting marks.

Melt one bag of white candy melts according to package directions. Dip the bottom of each bar lightly in the liquefied candy melt. Set bars on parchment paper or silicone mats and allow the candy coated cookie bottoms to cool and set. This happens fairly quickly. Reserve any left-over white melted candy for use in the next step.

Add the remaining bag of white candy melts to the bowl or pan with the reserved previously melted candy. Melt as before according to package directions. Dip the bars, top side facing down, into the melted candy, deep enough to cover the top and sides of the bars. Lift the bar out of the melted candy and allow excess to drip off of the end of the bar. Set coated bar on parchment paper or silicone mat and allow the candy coating to dry completely.

When dry and firm, with a sharp knife, trim off excess hardened candy coating that extends beyond the bottom margins of the bars.

Melt colored candy melts per package instructions. Drizzle melted candy over bars as desired. Allow bars to dry. Store, covered, at room temperature.