Preheat oven to 325 degrees F and line an 8"x8" pan with parchment paper.
In a large bowl, whisk together melted butter and sugar until glossy and smooth.
Whisk in whole egg, egg yolk, cream cheese, and vanilla extract until well combined.
Mix in flour, strawberry powder, and salt until just combined, taking care not to over-mix.
Spread about ⅔ of batter into prepared pan.
Dollop spoonfuls of strawberry swirl mixture over the batter.
Top with spoonfuls of remaining batter (don't worry if it doesn't completely cover jam).
Use a knife to gently swirl batter and jam
Bake for 34-38 minutes, until edges are just set, but center still has a slight jiggle.
Let cool completely before removing from pan and slicing.