Preheat oven to 350° and line a 9"-x-9" pan with parchment paper. In a large bowl using a hand mixer, beat butter and both sugars until light and fluffy. Add eggs and vanilla and beat until combined.
In a medium bowl, whisk together flour, baking powder, and salt. Add dry ingredients to wet ingredients and beat until just combined.
In another medium bowl using a hand mixer or whisk, beat cream cheese, sugar, egg, and lemon zest (if using) until smooth.
Place jam in a microwave-safe bowl and heat until pourable, 20 to 30 seconds.
Press ⅔ blondie batter into prepared baking pan. Add dollops of cream cheese mixture and jam all over the surface of blondie, then top with dollops of remaining blondie batter. Use a butter knife to swirl ingredients together, then bake until brownie is golden and cooked through, about 35 minutes.
Recipe by 5* trending recipes with videos at https://food.theffeed.com/2019/02/07/cheesecake-blondies/