To brown the butter, place sticks of butter in a deep sauce pan over medium heat, stirring frequently, until melted and starting to foam. Watch for brown specks to start to form on bottom of pan and the melted butter has darkened slightly and has a nutty aroma. Remove from heat, transfer to a bowl and cool to room temp. This all takes about 35 min. 

Preheat oven to 350Deg F, prepare two cupcake pans with paper or foil liners

In a small bowl sift together the flour, baking powder and salt, set aside. 

Combine the milk and sour cream in a cup and mix well. 

In bowl of a stand mixer, mix the eggs and sugar together on medium speed until thickened and lighter in color. Add in the cooled brown butter, bourbon and vanilla and mix well. 

Alternate adding the flour mixture and milk/sour cream mixture starting and ending with the flour mixture over low speed until just combined. Don’t over mix

Fill cupcake pan ¾ way full each cup. Bake for 16-18 min, depending on oven temp (mine runs hot so they’re done at 16 min). Check for doneness by lightly pressing the top of one and see if it bounces back

Cool 5 minutes in pan

While cooling 5 minutes, pour the cinnamon chips in a bowl. Dip the tops of each cupcake in the chips, pressing lightly. Let cool completely on a wire cooling rack

Set a pan of water over medium heat and bring to a simmer

In bowl of stand mixer combine the 6 egg whites, salt and sugar. Make sure that there aren't any egg shells or yolk in the whites. Set the bowl over the pan of simmering water, making sure the bowl doesn't touch the water, clip a candy thermometer to the side with the end just submerged in the mixture. Whisk constantly until the mixture reaches 160 degF and remove immediately.

Place the bowl back in the stand mixer and using the whisk attachment slowly bring up the speed to medium high and beat the mixture until the bowl is cool to the touch and has thickened and increased in volume and turned white. This takes about 7-10 min

Once cool, lower the speed to medium, and add in the butter pieces one at a time until all mixed in. It may get soupy looking but that is OK. Once all the butter is mixed in turn the speed up to med-high and whip until you see a change in consistency and hear the mixture making a whipping sound. You will hear a change in the way it sounds – and it will look thicker and fluffier.

Change to the paddle attachment. Add in the vanilla extract and mix on medium until combined. Add the pumpkin puree ¼ c at a time mixing well after each addition. The buttercream shouldn't change consistency with the addition of the pumpkin this is why it is best to add in ¼ c at a time. Stir on low once all the pumpkin is added in to get the air bubbles out. It is now ready to spread or pipe on cupcakes or a cake. Can be stored at room temp if using same day, if not cover tightly and refrigerate until ready to use. Bring to room temp and whip again in mixer to get it back to the right consistency before using.

Once cooled, frost with pumpkin buttercream.  These are best eaten at room temperature. These will keep up to a week, stored in the refrigerator. Thaw at room temp 30 min before eating, they are even better the second day!