Step 1

Place a rack in center of oven; preheat to 350°. Place ½ cup peanuts on a cutting board and use the bottom of a medium saucepan to crush them into smaller pieces; set aside.

Step 2

Butter bottom and sides of an 8x8" glass or metal baking dish. Sprinkle baking dish with a light dusting of flour, then invert and tap out excess flour.

Step 3

Melt ½ cup (1 stick) butter over medium-low heat in skillet you used to crush peanuts. Let cool.

Step 4

Whisk 1¼ cups flour, ¾ tsp. baking powder, and ¾ tsp. salt in a medium bowl.

Step 5

Add 2 eggs, 2 tsp. vanilla, ¾ cup peanut butter, and 1½ cups brown sugar to cooled butter and whisk until smooth.

Step 6

Add dry ingredients to peanut butter mixture and stir with a rubber spatula until flour disappears, then fold in half of peanuts. Scrape batter into prepared pan (hold on to the saucepan) and use spatula to work batter into corners.

Step 7

Melt remaining 3 Tbsp. butter, 3 Tbsp. peanut butter, and 2 Tbsp. brown sugar in reserved saucepan over low heat, stirring, until smooth.

Step 8

Using the back of a spoon, create deep divots all across top of batter. Pour mixture from saucepan into divots, letting it spill out and across surface of batter.

Step 9

Sprinkle remaining half of crushed peanuts over. Bake blondies until a tester inserted into the center comes out greasy but clean, 30–35 minutes.

Step 10

Let cool, then cut blondies into squares.

Step 11

Top blondies with ice cream and sprinkle with more peanuts.