For the cupcakes:
Preheat the oven to 350°F. Toast the pecans on a baking sheet for about 5-7 minutes. Cool the pecans and then chop into fine pieces.
Using a stand mixer, blend the sugar, brown sugar, vegetable oil until well combined. Add in eggs and egg yolks and beat on medium speed until the eggs are well incorporated and the batter is lighter in color, about 2 minutes.
Next mix in the sour cream and beat until well combined.
In a medium sized bowl, whisk flour, baking powder, soda and salt. Add vanilla to the buttermilk. Then, add 1/3 of the dry ingredients to the batter followed half the buttermilk and beat until it starts to combine. Alternate adding the remaining flour and buttermilk, starting and ending with the flour. Blend until just combined.
Add the chopped pecans and fold into the cupcake batter. Using a large ice-cream (cookie) scoop, fill each cupcake liner 2/3 full.
Bake at 350°F for 18 minutes, turning halfway through.
Using the paddle attachment, whip butter for 5-7 minutes, scraping down the bowl occasionally. Beat until butter looks light in color.
Add 3 cups of powdered sugar and mix on low speed until incorporated into butter then add the vanilla extract and cinnamon, mix to combine. Add 2 cups of powdered sugar and 1 Tablespoon of the heavy cream. Beat on low speed until sugar is incorporated. Add remaining powdered sugar and another tablespoon of the cream. Beat on low until the sugar in incorporated. Increase speed to medium-high and beat for 2-3 minutes.
If the frosting is too thick, add an additional tablespoon of heavy cream and continuing beating until fluffy.
Frost the cooled cupcakes and garnish with crushed pecans.