Heat the oven to 350F.

With electric mixer, cream butter and sugars on medium high for 2 to 3 minutes until fluffy and pale yellow in color. Scrape down the sides of the mixing bowl with a spatula.

On a lower speed, add egg yolks to incorporate. Increase the speed back up to a medium high for 1 to 2 minutes until the sugar dissolves and the mixture is a pale white color.

Lower mixer speed once more, then add the flour, oats, baking powder, baking soda, and salt. Mix until your dough comes together and the dry ingredients have incorporated. The dough will be a stiff, buttery, almost greasy dough, not like a typical cookie dough.

Pam spray a foil-lined sheet pan. Plop the oat cookie dough in the center of the pan and spread it out until it is 1/4" thick.  Don't bother trying to use a spatula, just mash it down with your hand.  If it starts sticking to your palm too much, moisten your hand a little with some water. The dough won't end up covering the entire pan, this is okay. Bake the oat cookie at 350F for 15 minutes and cool completely before moving to next steps.

Heat oven to 350F.  Break the oat cookie into smaller chunks.  Put the oat cookie, brown sugar and salt in the food processor and pulse it on and off until the cookie is broken down into a wet sand. (If you don't have a food processor, you can fake it till you make it and crumble the oat cookie diligently with your hands or bash it in a plastic bag with a rolling pin).

Transfer the cookie crumbs to a bowl and, with your hands, knead the butter and ground cookie mixture until the contents of the bowl are moist enough to knead into a ball. If it is not moist enough to do so, gently melt and additional 15-25g of butter and knead it into the oat crust mixture.   Pour crust mix into a spring-form pan.

Using your fingers, gently level out the oat crust.  Once you have things starting to look even, use a round, flat-bottomed jar to firmly press the crust into the bottom and sides of the pan.  Bake for 12-15 minutes and let cool completely before adding the filling.

Chill a medium mixing bowl and electric beaters in the freezer for 15 minutes.  Remove from freezer and whip cream until it's stiff.

In separate bowl, beat cream cheese, vanilla, and sugar until it is soft and fluffy.

Add whipped cream to cream cheese mixture and combine until completely mixed and smooth.  Pour into oat cookie crust and chill for at least 4 hours before adding the topping and slicing.