Preheat the oven to 350°. Spread the pecans on a rimmed baking sheet and toast until fragrant, 8 to 10 minutes. Let cool completely. Coarsely chop and set aside.
Combine the flour, baking powder and salt in a medium-size bowl. Set aside.
Cream the cooled melted butter, 1 cup of the brown sugar and the granulated sugar together in a large mixing bowl with a wooden spoon until smooth.
Add the egg and vanilla extract and beat until smooth.
Stir in the flour mixture until just incorporated.
Place the bowl in the refrigerator for 10 minutes (or up to 6 hours) to let the dough firm up.
Drop the batter by heaping tablespoonfuls onto ungreased baking sheets, leaving about 3 inches between each cookie. (Balls of dough may be placed next to each other on parchment paper-lined baking sheets, frozen, transferred to zipper-lock plastic freezer bags and stored in the freezer for up to 1 month. Frozen cookies may be placed in the oven directly from the freezer and baked as directed.)
Bake the cookies until golden around the edges but still soft on top, 12 to 14 minutes (a minute or 2 longer for frozen dough).
Let the cookies stand on the baking sheet for 5 minutes, then remove them with a metal spatula to a wire rack to cool completely.
Place a rimmed baking sheet under the wire rack.
In a small saucepan, combine the remaining 1 cup light brown sugar with the heavy cream. Bring to a boil over medium heat.
Turn down the heat and simmer, stirring constantly, for 3 minutes.
Remove from the heat and whisk in the confectioners sugar.
Stir in the pecan pieces.
Spoon a scant tablespoon of the pecan mixture onto each cookie.
Let stand until the praline is set, about 1 hour.