Preheat oven to 350. Carefully line a 9" square baking pan with heavy-duty aluminum foil, letting the foil extend up the sides and over the edges of the pan. Butter the foil liner.
To make crust: In a large bowl, stir together flour, brown sugar and salt until blended. Using a pastry blender or 2 knives, cut the butter into the dry ingredients until mixture forms large, coarse crumbs the size of small peas. Press the crumb mixture into the bottom of prepared pan. Bake the crust until the edges are lightly browned and the top feels firm when lightly touched, 12-17 minutes. Set aside.
To make filling: In a saucepan over medium heat, combine the butter, maple syrup and brown sugar; stir together until the butter melts and brown sugar dissolves. Bring to a boil and boil for 1 minute. Remove from heat and immediately stir in the cream. Then stir in the pecans. Pour the hot filling over the partially baked crust, spreading it evenly to the edges with a spatula.
Bake on middle oven rack, until the filling is set when you give the pan a gentle shake, 22-25 minutes. During baking, the filling will bubble vigorously, then the bubbles will subside and become smaller toward the end of baking. Transfer to a wire rack to let cool until firm, about 1-1/2 hours.
Using the ends of the foil liner, carefully lift the maple pecan square in its liner from the baking pan. Run a small knife around the edges of the square to loosen it from the foil. Using a large, sharp knife, cut into 25 small squares. The squares will easily slide off the foil.
Store in an airtight container at room temperature for up to 3 days.