Combine the chopped peaches, sugar and sifted cornstarch in a cast iron pan.

Set aside until you cook the cake layers in the Traeger. You'll then smoke the peach mixture while you bake the cakes. 

In a medium sized saucepan, brown the butter over medium heat on your stove. You want the butter to boil and start to pop. At this point, the butter will also start to cook. Keep a close eye on it and let it cook until it's browned and has some dark specs. Remove from heat and let cool back to room temperature. I suggest putting the butter in a bowl and refrigerating it so it can harden slightly, or making the browned butter a day ahead. 

In the bowl of a stand mixer fitted with a paddle attachment, combine the cooled butter, oil, sugar and salt. Beat on medium speed for about 2 minutes, until light and fluffy.

Turn the mixer to medium-low and add the eggs and egg yolks, one at a time, scraping down the sides of the bowl in between each addition.

With the mixer on low, alternately add the flour and baking powder with the buttermilk, starting and ending with the flour. Mix until combined.

Add the butter extract and vanilla extract. Mix on low until combined.

Bake the cakes on the Traeger for about 23 to 25 minutes, until a toothpick inserted in the center of the cakes comes out with only just a few crumbs on it. At this point, you'll also want to put the peaches on the Traeger as well. The peaches will cook for about 40 to 45 minutes. 

Cool the cakes on wire racks for about 10 minutes. Carefully invert the cakes onto cooking racks to cool completely. If you don't plan to stack and decorate the cake right away, level the cakes if needed and then immediately wrap each layer in plastic wrap or tin foil and freeze. 

About an hour before assembly, remove the cake layers from the freezer.

Let the peaches cool completely before using in the cake.

Preheat your oven to 375 degrees F. Line a baking sheet with parchment paper and set aside.

In a medium bowl, combine the oats, brown sugar, flour, butter, cinnamon and salt. Mix by hand with a wooden spoon until the mixture resembles clumps of sand. Spread the crumble over the parchment paper and bake for 8 to 10 minutes, stirring halfway through. The crumble should be golden brown. Let it cool completely and then crumble the mixture into smaller pieces, if needed.

In the bowl of a stand mixer fitted with the paddle attachment cream the butter on medium speed for about 3 minutes, until the mixture is light and fluffy.

With the mixer on low speed, slowly add the powdered sugar, followed by the heavy cream, vanilla bean paste, vanilla extract and dash of salt.

Continue to beat the frosting on medium-high speed for an additional 5 minutes.    

Before frosting your cake, mix the frosting by hand with a wooden spoon to push out the air pockets.

Place the first cake layer, top side up (crumb side up), on a cake board or cake plate. Using an offset icing spatula, spread a thin layer of frosting over the cake layer. This creates a barrier between the cake and peach filling so the cake doesn't become soggy. 

Pipe a rim of frosting around the edge of the cake layer. This will help support the cake layers and prevent the peach filling from spilling out. (You may even need to pipe a second time over the first rim you made).

Spread about half of the peach filling on the cake layer. 

Sprinkle about half of the crumble over the peach filling.

Gently place the second cake layer on top of the filling and crumble and repeat steps 2 to 4.

Place the final cake layer top side down on the second layer of filling. 

Freeze the cake for about 10 minutes to help set the frosting and filling, making it a bit more stable for when you frost. If the cake still feels wobbly, add a dowel to the center of the cake (or you can even use drinking straws for this).

After the filling is set, use a small amount of frosting to apply a crumb coat around the entire cake. Freeze the cake again for another 10 minutes to set the crumb coat.

After the crumbs are locked in, continue to frost and decorate the cake.

Save remaining crumble and compote to serve on the side of each cake slice.