1. Line an 8-inch (20 cm) square pan across the bottom and up the sides with two sheets of aluminum foil, making a big criss-cross with the sides overhanging.
2. Preheat the oven to 325F (160C) and position the rack in the center of the oven.
3. In a large bowl, toss together the flour, baking powder, baking soda, and salt. Add the brown sugar, walnuts, dates, and apricots. Use your fingers to mix the fruit, separate any pieces sticking together.
4. Beat the egg and vanilla in a small bowl, then mix it with the fruit and nut mixture until everything’s coated with the batter. Spread the mixture in the baking pan and press gently to even it out.
5. Bake for 35-40 minutes until the top of the bars are golden brown and has pulled away just-slightly from the sides of the pan. Cool the bars in the pan, then lift out.
6. To cut the cooled bars, use a heavy sharp knife, such as a bread knife, for best results in getting clean slices.