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1
Heat the oven to 350F.
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2
Combine the butter and sugars in the bowl of a stand mixer fitted with the paddle attachment and cream together on medium-high for 2 to 3 minutes, until fluffy and pale yellow in color.
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3
Scrape down the sides of the bowl with a spatula.
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4
On low speed, add the egg yolk and increase the speed to medium-high and beat for 1 to 2 minutes, until the sugar granules fully dissolve and the mixture is a pale white.
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5
On low speed, add the flour, oats, baking powder, baking soda, and salt.
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6
Mix for a minute, until your dough comes together and any remnants of dry ingredients have been incorporated.
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7
The dough will be a slightly fluffy, fatty mixture in comparison to your average cookie dough.
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8
Scrape down the sides of the bowl.
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9
Pam-spray a quarter sheet pan and line with parchment, or just line the pan with a Silpat.
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10
Plop the cookie dough in the center of the pan and, with a spatula, spread it out until it is 1/4 inch thick.
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11
The dough wont end up covering the entire pan; this is OK.
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12
Bake for 15 minutes, or until it resembles an oatmeal cookiecaramelized on top and puffed slightly but set firmly.
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13
Cool completely before using.
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14
Wrapped well in plastic, the oat cookie will keep fresh in the fridge for up to 1 week.
