Brown the butter by heating a stick of butter in a saucepan over medium heat, while stirring intermittently. It will melt, bubble, foam and then the milk solids will toast and settle on the bottom.

Allow the butter to cool back to room temperature (stir often cooling in the refrigerator).

Make sure to read my whole post on browning butter if you haven’t done it before.

Preheat the oven to 350F/177C convection (325F/163C conventional) and grease and line three 6 inch cake pans.

In a medium bowl, whisk together the flour, baking powder, cinnamon and salt until they're evenly distributed.

Place the room temperature brown butter, the oil and the brown sugar in a large bowl and use an electric mixer with the whisk attachment to beat them for 2 minutes.

Add the eggs, one at a time, beating on medium speed until each egg is fully incorporated. Add the vanilla extract and sour cream and beat just until combined.

Add half of the dry ingredients to the wet ingredients, turn the mixer on low speed and then pour in the milk, followed by the rest of the dry ingredients.

Distribute the batter evenly among the three cake pans, about 14oz in each pan and bake for 30-35 minutes. When the cake is fully baked it will release itself from the edge of the pan and it will spring back if you press on the center of it.

Allow the cake to cool completely before frosting.

Heat the cream over medium heat until it comes to a simmer (bubbling all around the edge).

Pour the cream over the chips and cover the bowl with a lid or plastic wrap for about 5 minutes, so the they melt.

Use a whisk to gently stir the ganache until it's completely smooth.

Cover again and allow it to cool completely to room temperature. You can refrigerate to speed up the process but make sure to stir it every 5-10 minutes so it cools evenly.

Remove 3/4 cup (6oz) of the ganache and set it aside in a smaller bowl.

Use the whisk attachment of an electric mixer, at full speed, to beat the ganache in the large bowl for 3-5 minutes, until the ganache has lightened in color and grown in volume.

Scrape the edge of the bowl, add the butter and beat the ganache just until it's shiny like buttercream. Use a rubber spatula or the paddle attachment at low speed to beat press out excess air bubbles.

Place the first layer of cake onto a flat surface and spread a layer of whipped butterscotch ganache onto the first layer of cake.

Repeat with the next layer and then place the third layer on top. Make a little crumb coat by frosting the outside super lightly and then refrigerate the cake for 15-30 minutes.

Use the rest of the whipped ganache to frost the cake. I place it all on top and work my way down the sides of the cake with an offset spatula.

Once the cake is covered, use a cake scraper to smooth out the ganache. Then run the cake scraper under super hot water and go around the ganache really slowly and gently to get it as smooth as possible. Refrigerate the cake for 15-30 minutes again. 

Reheat the reserved, unwhipped butterscotch ganache, for about 10-15 minutes, just until it’s a little runny. Spread the ganache on top of the cake, allowing it to drip off the edge.

If it’s too runny, it’ll run down quickly, if it’s cooled too much it won’t drip. If it’s right in the middle, it’ll run off the edge but still let you create those swirls on top. Top with a pinch of sea salt flakes.