Whisk together 1 ¼ cups all-purpose flour, 1 tsp. baking powder, and 1 tsp. kosher salt. Whisk together 2 large eggs, 1 ½ cups light brown sugar, ¾ cup smooth peanut butter, ½ cup melted unsalted butter, and 1 tsp. vanilla extract; fold in dry ingredients. Scrape batter into a buttered 8x8" baking pan. Dollop with 2 Tbsp. strawberry jam; top with 1 Tbsp. chopped honey-roasted peanuts. Bake at 350° until a tester comes out clean, 35-40 minutes. Sprinkle with flaky sea salt.