Cream together the butter, sugar and salt (if using) in a large bowl, or a stand mixer fitted with a paddle attachment, until the mixture is light in colour and fluffy.
Add the egg yolks one at a time and mix thoroughly.
Mix in the vanilla extract and dandelion flower petals.
Pour in the flour and mix until the dough is well combined and smooth.
Remove the dough from the bowl and roll it into a log.
Mix together the remaining 1/4 cup of sugar and 2 Tbsp. of dandelion flower petals and sprinkle onto a clean surface (counter or cutting board).
Roll the dough log over the sugar and petal mixture.
Wrap the log in parchment paper or plastic wrap and place it in the fridge for a least one hour or overnight.
Using a sharp knife, cut the log into 1/4 inch slices and lay them on a parchment lined baking sheet.
Bake at 350F for 10 to 12 minutes or until the edged of the cookie just begin turning light brown.