In a med bowl, combine AP flour, custard powder, baking powder and salt. Whisk to combine and set aside.
In a measuring cup, combine milk, egg yolk, vanilla extract, and the caviar of the whole vanilla bean. Stir to combine and set aside. (Note - Vanilla caviar may not combine well, but it will when you add it to the butter mixture below).
Using a hand or stand mixer, beat butter, then add sugar and beat until fluffy. Add the milk mixture and beat until they come together. May take a minute or so.
Turn mixer down to low and add in the flour mixture (dry ingredients) until it forms a dough and has pulled away from the sides of your mixing bowl. Turn the dough out and divide into approx two 4 x 6 squares, about an inch or so thick. Wrap in plastic and chill. (I like to chill overnight, but you can also chill these for 1 or 2 hours, then use.)
This recipe is made with the “Sweet Strawberry” House on the Hill cookie mold, however you can use the mold of your preference. It is best however to use a cookie mold that has a shallower depth, because the thicker the cookie, the longer it will need to be baked, and the longer they are baked, the browner the edges will become. You don't want these super brown or over crisp.
For the Cookie Tops - To make sure the deep strawberry part of the cookie mold is filled with dough - I roll out just enough dough for 1 cookie to about 1/2 inch deep, then lay my dough over the cookie mold and press it in. Where the strawberry is on the mold - press the dough into the strawberry all around the edges, to make sure no cracks form in the strawberry part. Once you do this, it will not have enough dough, so I take a small ball of dough to fill it, and press it into the back, on top of the dough I have already pressed, then take my rolling pin and roll it so that it’s all even. I then turn the whole thing over so that the mold is on top, and press it down to my desired depth. Then carefully remove the mold, and use a scalloped round cutter the same size as mold to cut around the strawberry.
For the Cookie Bottoms - Roll dough to approx 3/16” or your desired thickness, then cut with the round scalloped cutter to match the tops. No need to use the cookie mold on the bottom cookies. Make the same amount as you have for the tops.
Once all of your top and bottom cookies are pressed and cut, place them on a parchment lined baking sheet and chill for at least 20 min before cbaking.