PREPARE THE TOPPING To a food processor, add the 60 g Sugar, 1 Tbsp Custard Powder*, 1/2 tsp salt, and 1/2 tsp baking powder. Blitz for about a minute, then add 120 g all purpose flour and blitz again. Add the 60 g Unsalted Butter and pulse until the butter completely "disappears" into the mixture — it'll have the texture of lightly wet sand. Add 2 Egg Yolks and 1/8 tsp almond extract and continue processing just until the mixture pulls together.
Dump the loose dough onto a large piece of plastic wrap and firmly but swiftly press the pieces together, kneading lightly if needed, to form a more cohesive dough. Wrap the dough in the plastic and roll into a neat log shape. Refrigerate at least 1 hour.
MAKE THE COOKIE DOUGH Add 225 g butter to a medium-sized, light colored pot or pan. Heat on medium until butter melts, then stir, scraping the bottom constantly, with a heatproof spatula until you see brown bits at the bottom of the pan. This browning process can happen quickly and may end up burning if you're not watching carefully! As soon as the butter solids turn light brown, pour the butter into a medium-sized mixing bowl to help stop the cooking.
Add 250 g granulated sugar, 50 g brown sugar, and 1 tsp kosher salt to the hot butter and carefully stir to combine. Let rest at cool room temperature for about an hour until the mixture starts to congeal. If your kitchen is warm you can do this step in the refrigerator but you'll want to make sure the mixture remain soft and doesn't completely harden.
Give the cooled mixture a stir to "fluff" it up. Add 1/4 tsp baking powder, 1 tsp baking soda, and 1 Tbsp dry milk powder, and mix to combine well. Add 1 egg, 1/4 tsp vanilla extract, and 1/8 tsp almond extract and mix well to combine before adding the 250 g bread flour and gently folding it in. Once flour is moistened, mix well to combine.
ASSEMBLY AND BAKING Remove topping from the refrigerator, unwrap, and carefully slice into 12 discs. Set aside. Scoop egg-sized balls of dough and roll between your hands to achieve a smooth ball (I use a ~2 Tbsp cookie scoop for this). Place balls 3" apart on a parchment-lined baking sheet.
Taking one disk of topping between your fingers, gently pinch, press, and rotate the disk until it's about 2" in diameter (quite a bit larger than the diameter of the dough balls). Dust your fingers and work surface lightly with flour if you experience any sticking. Gently drape the topping circle over each dough ball.
To make the egg wash, mix 1 egg yolk, 1 tsp water, and a Pinch salt in a small dish. Brush the top of each topping layer with egg yolk mixture. Bake for 12 minutes at 350F, then turn on the top broiler of your oven to 450F and broil for 2-3 minutes until the bolo topping starts to brown. Keep an eye on your cookies here and move the pan around as necessary to ensure each cookie receives some color — you may leave the oven door open during this step as well.
Remove cookies from oven and wait 5 minutes, then transfer each cookie to a cooling rack to finish cooling. I find these are best enjoyed once completely cool, as it gives the bolo topping time to firm up correctly.