Preheat oven to 350°F. Line a 13x9-inch pan with parchment paper.
In a large bowl, cream the butter and brown sugar until light and fluffy. Stir in the eggs, one at a time, until combined. Stir in the vanilla.
Add the flour, baking powder, and salt, and stir just until combined. Stir in the chopped nuts.
Spread the dough into the prepared 13x9-inch pan.
Bake for 22–26 minutes, or until lightly brown on the edges and the center no longer looks raw.
Let cool completely then cut into bars.
Notes
Don't want pecans? Try walnuts, macadamia nuts, chopped Oreos, M&Ms, chocolate chips, butterscotch chips, white chocolate chips, shredded coconut, or dried cranberries instead. You can also top them with jimmies-style sprinkles before baking.Store any leftovers at room temperature for up to one week. You can also freeze the bars for up to 3 months.