Preheat oven to 350°F (180°F). Line a baking tray with parchment paper.
Whisk flour, baking powder, and salt together in a medium bowl.
Beat butter and sugar together in a large bowl until light and fluffy, about 3 minutes. Add vanilla, 1 whole egg and 1 egg yolk (reserve the egg white). Beat well.
Mix dry ingredients into wet ingredients until just combined. Arrange pecan pieces on prepared baking tray in groups of 5, to resemble head, arms and legs of a turtle.
Lightly beat reserved egg white in a small bowl. Shape cookie dough into 1 inch balls. Dip bottom of balls in egg white and lightly press onto grouped pecans. The tips of pecans should be seen. Bake for 10-12 minutes, or until edges are light golden brown. Remove from oven and let cool completely on a wire rack.
Stir melted butter and cocoa powder together in a small bowl until combined. Add sugar, milk, and vanilla extract, and mix until combined and smooth.
Frost tops of cooled cookies. Let the frosting set before storing in an air tight container for up to 5 days.
Salted butter can be substituted. Omit the extra salt in the recipe.
Since only a little is needed, whole milk, 2% or 1% milk can be used.
Pecan halves are best used for this recipe since you only need to cut them in half. Pecan pieces would be too tiny, and full pecans would be too large. Cutting them into 4 would not be easy.
Lightly press the cookie balls into the pecans. You don't want to flatten the balls.
Make sure the pecans are sticking to the cookie ball.
Make sure that you can see pieces of pecan after placing the cookie ball on top. The cookie will spread only a little while it bakes.