Step 1Combine butter and granulated sugar in bowl of electric mixer. Add eggs 1 at a time. Beat until creamy. Add maple syrup and extract. Mix well. Add baking powder, pecans, flour and salt. Mix until just combined, scraping down sides of bowl. Batter can be used immediately or refrigerated overnight.
Step 2Generously grease madeleine molds including rim around each mold, then dust with flour, tapping out excess. Use tablespoon-size measure to transfer batter into each mold; it should be three-quarters full. If baking separate batches, batter can be kept at room temperature.
Step 3Bake at 400 degrees until edges are browned and domed tops spring back when pressed lightly in center, about 10 minutes (30 to 60 seconds longer if batter was chilled). Do not overbake. Spread clean towel on counter. Remove pan from oven, immediately hold it by opposite edges, turn it over and tap it on towel until madeleines fall out. Transfer madeleines to rack to cool. For batches, repeat preparation of pan (wash it first) and bake remaining batter. (Can be served immediately or made ahead and stored at room temperature for 1 day in an airtight container or frozen 1 month wrapped airtight.) To serve, lightly sprinkle shell-side of room temperature (or warm-from-the-oven) madeleines with powdered sugar.