Preheat oven to 350 degrees. Spray a 9x13 baking pan with cooking spray or line the pan with parchment paper.
In a large bowl, whisk together melted butter and sugars.
Add eggs and vanilla extract and whisk until smooth.
Add flour, baking powder, and salt to the butter mixture and stir with a wooden spoon until combined. Batter will be thick.
Mix in ¾ cup of diced strawberries and ¾ cup sliced rhubarb.
Pour batter into the prepared pan and spread evenly.
Sprinkle top with remaining strawberries and rhubarb.
Bake blondies for 30-35 minutes or until a knife is inserted and comes out clean.
Cool completely. You can drizzle the top of the bars with melted white chocolate if you'd like.
*Sometimes we add chopped white chocolate into the blondies. About 5 ounces of chopped white chocolate would be a good amount.The calories shown are based on the recipe being cut into 15 pieces, with 1 serving being 1 blondie bar. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate. **We are not dietitians and recommend you seek a nutritionist for exact nutritional information.**