Adapted slightly from Piece of Cake. Yes, Gwen, you can probably substitute margarine for the butter but why? If you must, might I recommend Earth Balance? Love that stuff. I use it on the table instead of butter but I cook and bake with butter. Anyway, you came here for the recipe and not the product plug, right?
2 sticks unsalted butter, softened but still cool
1 cup granulated sugar
3/4 teaspoon salt
1 teaspoon pure vanilla extract (TJs sells bourbon vanilla extract that is great here)
2 cups all-purpose flour
1 C honey roasted peanuts, roughly chopped
Preheat oven to 375.
In a large bowl, cream together sugar and butter for about 2 minutes or until light and fluffy. You can use a hand mixer for this. Honestly, I don't even bother to get out my kitchen aid for something this easy. Add salt and vanilla and mix until combined. On low speed, mix batter while you incrementally add flour. Watch out for a flour snow storm; keeping your mixer on low will help. Once flour is thoroughly incorporated, add one half of the peanuts and stir until just mixed.
Shauna recommends a 15.5 x 10.5 pan but I don't have one so I just used my largest sheet pan and didn't spread the dough to all 4 corners. Press dough into an even layer and then sprinkle on remaining peanuts. Press in with your hands or a measuring cup. Bake for 20-25 min and rotate pan halfway through baking. Really watch the cookies after you rotate b/c my oven seems to be running hot these days and burnt the edges (oops). You want these cookies to be lightly browned but even medium brown still tastes mighty good. Allow to cool for 5 minutes before cutting into squares with a knife or pizza cutter. Or you can allow to cool completely and then break them up by hand like you would with peanut brittle. When cool these will have a brittle-y consistency and they taste so good. You could sub regular peanuts or another kind of nut if you wish. I think peanuts are perfect, tho. Store in an airtight container if they last that long.