Preheat the oven to 350°F. Spread the pecans on a small cookie sheet and toast at 350°F for 10-12 minutes, checking them frequently to make sure they aren't burning. Let the pecans cool briefly. (If you're using pecan halves, chop them into smaller pieces.)
While the nuts are toasting, pour the caramels, milk, and butter into a saucepan and set over medium to medium-low heat, stirring frequently until the caramels are melted and smooth. Add additional milk if the caramel is excessively thick.
While the caramel is melting, fill a saucepan with a couple inches of water and bring to a gentle simmer. Line two 9x13-inch cookie sheets with parchment paper and trace sixteen 3-inch circles on the paper.
Arrange the chopped pecans in piles inside the circles. Place a cookie cutter over each pile and swirl it gently to push in stray nuts and make the edges nice and smooth. Spoon the melted caramel on top of the pecans, leaving a border of nuts around the edge.
Pour the chocolate chips into a heatproof bowl and set over the saucepan of gently simmering water. Be careful not to let the bottom of the bowl touch the hot water, and keep the steam away from the chocolate. Stir occasionally until it is fully melted.
Let it cool for a few minutes, then pour into a sandwich bag and snip off the tip to create a little piping bag. Pipe a circle of chocolate on top of each turtle, leaving a border of caramel around the edge.
Chill the turtles for 10 minutes, then use an angled spatula or butter knife to create a decorative swirl on top of each turtle. Sprinkle with flaky salt if desired; then chill for another 20 minutes, or until quite firm. Serve at room temperature to make them easier to eat.