Preheat your oven to 350°F (177°C). Line a cookie sheet with parchment paper or a silicone mat and place to the side. In a large bowl (or stand mixer with a paddle attachment), cream together the unsalted butter and brown sugar until light and fluffy, about 2-3 minutes.
Beat in the egg yolk and vanilla extract.
In a separate bowl, combine flour, cocoa powder, and table salt. Add this flour mixture to the wet ingredients and mix until a soft cookie dough forms. Cover with plastic wrap and chill for 30 minutes for easier handling.
Use a cookie scoop to portion about 1–2 tablespoons of dough. Roll dough into 1-inch balls, dip in whisked egg whites, then roll in pecans. Place 2–3 inches apart on the prepared baking sheet.
Gently press your thumb into the center of each ball to form an indent or I like to use the back of a ¼ teaspoon. Bake for 10–12 minutes, until just set. Transfer to a cooling rack.
In a small bowl, microwave caramels with cream in 20-second bursts, stirring until smooth. (Or make them extra indulgent with my Homemade Soft Caramels.) Spoon into the centers of each cookie. Let sit for 2-3 minutes to set. Stovetop Method for Melting Caramels: Place your caramel pieces (or Homemade Soft Caramels) and the heavy cream into a small saucepan. Set over low to medium-low heat and stir constantly with a heat-proof spatula or wooden spoon. Keep the heat gentle — caramels scorch quickly if the pan gets too hot. Stir until smooth and creamy, then spoon into your baked cookie centers. NOTE: If the centers of your cookies puff up while baking, gently press them back down with the back of a ¼ teaspoon to make the perfect well for the caramel filling. Melt chocolate chips or dark chocolate in a double broiler, then drizzle over the tops.