Preheat the oven to 325 degrees.
Butter three 8-inch round cake pans, line the bottoms with parchment paper, and butter the parchment. Dust with flour, and knock out the excess flour.
Sift remaining flour and combine with baking powder and salt and set aside.
In the bowl of an electric mixer fitted with the paddle attachment, beat the butter and 1 ¼ cups of the sugar on medium speed until fluffy, about 3 minutes. Scrape down bowl and add yolks one at a time, beating briefly after each addition. Add vanilla and beat for 5 seconds. Turn mixer to low. Add flour mixture, alternating with milk in three additions, beginning and ending with flour mixture. Scrape down bowl and mix on low speed for a few more seconds.
In the bowl of an electric mixer fitted with the paddle attachment, beat yolks, sugar, and salt until combined. Add butter and beat on medium speed until combined. Gradually add cream and vanilla and beat just until combined. Pour the ingredients into a medium saucepan and cook over medium heat, stirring constantly, until the mixture is boiling. Continue to cook for about 1 minute until mixture is thickened and frothy (200 to 208 degrees on candy thermometer). Remove saucepan from heat, and stir in bourbon. Place filling over an ice bath until cool. Cover filling with plastic wrap and place in refrigerator while making the frosting. It is best that the filling be made one day ahead so it can chill overnight.
Note: you will fold in the pecans right before filling the cake (see “Assemble the Cake” below).
In a separate bowl, whisk egg whites until foamy, slowly add remaining 1/4 cup of sugar, and continue whisking until soft peaks form. Gently fold whites into batter.
Divide batter among prepared pans and smooth the tops. Bake for 30 to 35 minutes, rotating the pans halfway through the baking time, until a toothpick inserted in the center of each layer comes out clean. Transfer pans to cake racks and let cool for 20 minutes. Invert layers onto the racks, remove pans, and let layers cool completely. Remove parchment.
Place egg whites and cream of tartar in bowl of an electric mixer fitted with whisk attachment.
In a small saucepan, stir together sugar and water and cook mixture until it registers 242 degrees on a candy thermometer.
Just as the sugar mixture is about to reach 242 degrees (about 235 degrees), begin to whip egg whites and cream of tartar on medium speed. Remove sugar mixture from heat and pour it directly down side of the mixing bowl, being careful that sugar syrup doesn’t touch the moving whisk. Whip until stiff peaks form and the bottom of bowl is cool to the touch.
ASSEMBLE THE CAKE
Place one cooled cake layer on a serving platter. Trim the top to create a flat surface. Fold the pecans into the chilled filling. Evenly spread about 1 1/4-cups of the filling on top of the first cake layer. Top with the second layer. Trim the top and spread with the remaining filling. Top with the third layer and frost the sides of the cake using a palette knife, then the top of the cake. Be sure to use the frosting immediately after it is made, because the consistency will change as it sits, making it less easy to spread.
Let the cake set for about 15 minutes before serving.
NOTE: At Baked, the frosting is swirled in small peaks. Then, using a butane torch set on low heat, with a swaying motion three inches from the top of the cake, they lightly torch the top of the cake to add color.
This cake can be made one day ahead.