Step 1

Preheat oven to 350°F. Line a sheet pan with parchment paper.

Step 2

Combine 57 grams (4 tablespoons) of the butter, 38 grams (2½ tablespoons) brown sugar, and the granulated sugar in the bowl of a stand mixer fitted with the paddle attachment and cream together on medium-high until the mixture looks fluffy and pale yellow, about 2-3 minutes. Scrape down the sides of the bowl, add the egg yolk, and mix on medium speed until the sugar granules dissolve and the mixture looks very pale (closer to white than yellow), about 2 minutes.

Step 3

Turn the mixer to low speed, and add the flour, oats, baking powder, baking soda, and 1 gram (¼ teaspoon) salt. Mix just until the dry ingredients are fully incorporated, about 1-2 minutes. Dump the mixture onto your parchment lined sheet pan and flatten it out with your hands until it’s about ¼ inch thick. It won’t come close to filling the sheet pan, and it’s fine if it’s an irregular shape as long as the depth is mostly even (you’re basically making one very large oatmeal cookie). Bake until golden brown at the edges and set in the middle, about 15 minutes. Cool completely.

Step 4

When the cookie is cool, break it into pieces and add them to the bowl of a food processor. Add the remaining brown sugar and salt and pulse until the mixture is broken down into fine crumbs.

Step 5

Melt the remaining 27 grams (2 tablespoons) butter. Transfer the crumbs to a small mixing bowl and add the butter and mix until you can form the mixture into a ball. Press the mixture evenly along the bottom and up the sides of your pie tin and place on a sheet pan.

Step 6

Preheat oven to 350°F.

Step 7

In the bowl of a stand mixer fitted with a paddle attachment, add the both kinds of sugar, the milk powder, corn powder (if using) and salt and mix on low until combined. Add the melted butter and mix on low speed until the dry ingredients are moistened, about 2-3 minutes. Add the heavy cream and vanilla, and mix on low for another 2-3 minutes, or until the mixture looks homogenous with no streaks of cream remaining. Scrape down the sides of the bowl.

Step 8

Add the egg yolks, and mix on low speed for another 2-3 minutes or until the mixture is glossy and thoroughly combined. You don’t want to aerate the mixture–this is supposed to be dense, so keep the speed as low as your mixer will go and stop mixing as soon as the yolks have completely disappeared and the mixture looks homogenous.

Step 9

Spread the filling over the crust, and bake for 15 minutes. Open the oven door and reduce the temperature to 325°F. Keep an eye on the temperature (if you have an oven thermometer or an oven that notifies you of its temperature) and when it reaches 325°F, close the door and bake the pie for an additional 10 minutes (if you don’t have a precise way of monitoring your oven temperature, leave the oven door open for about 5 minutes and then shut it and bake 10 minutes). The pie should still jiggle in the middle, but look mostly set around the edges. If it still jiggles at the edges, bake for another 3-5 minutes.

Step 10

Transfer the pie to a wire rack to cool to room temperature. Then freeze it for at least 3 hours or overnight. (Well wrapped, the pie will keep for 5 days in the refrigerator or for a month in the freezer.) Transfer the pie to the refrigerator at least 1 hour before serving.

Step 11

Sift confectioners’ sugar over the top of the pie. Serve in small slices. Store any leftovers in the refrigerator.