- Preheat oven to 375 degrees.
- Whisk salt and flour together in medium bowl.
- Using stand mixer fitted with paddle attachment, place butter and sugar in bowl and mix on low until combined. Increase speed to medium and mix until light in color.
- Add yolks in 1 at a time, mixing after each addition. Add vanilla and mix until just combined.
- Add dry ingredients to butter mixture. Mix on low until dough forms.
- Lightly whisk egg white in small bowl.
- Roll dough into 1-inch balls. Dip each ball in egg white then roll in chopped pecans.
- Place balls on cookie sheet pan lined with parchment paper. Bake 4 minutes then remove from oven and indent with thumb to make small well in middle of each cookie. Return to oven and bake an additional 7 to 9 minutes, or until edges begin to brown.
- Remove from oven and let cool completely then place #2 tip in piping bag and fill with lemon curd (you can also fill a zip close bag with curd and cut off corner to use as piping bag). Pipe lemon curd into center of cookies and serve.
- Place sugar, lemon juice, yolks, and whole eggs in small non-reactive saucepan. Whisk to combine.
- Place over low heat and cook until mixture begins to simmer and thicken.
- Strain into a bowl through cheesecloth or fine mesh strainer then add cubed butter and stir until butter is melted. Place plastic wrap directly on surface of lemon curd and refrigerate to cool.