Grease the pan. For easy removal of the tart, place parchment paper on the bottom and 2 sides of the pan. Grease again and then set aside. You can also use an 8x8 pan, but just know the base will be thicker if you do.
In a medium-sized bowl, add cold butter, sugar, and flour. Mix until a crumb forms. This will be your streusel. Set aside.
3/4 cup flour, 1/4 cup white sugar, 4 tbsp butter
In a bowl, add in yolks, butter, flour, cornstarch, baking powder, and sugar. Mix with your hands until a dough forms.
1 1/4 cups flour, 1/3 cup butter, 2 egg yolks, 1 tsp cornstarch, 1/2 tsp baking powder, 1/4 cup white sugar
Transfer the dough into the pan and spread evenly. It will spread thin and may take a few minutes to do, rest assured this is normal. Make sure the entire bottom of the pan is covered evenly.
Take a fork and prick holes across the entire bottom and sides of the base. This makes sure that the steam accumulated while baking can leave and not cause the crust to puff up. Make sure to prick the bottom and sides.
Bake the crust at 350℉ for 15 minutes or until golden brown. Allow to cool as you prep the fruit layer.
In a medium-sized bowl, add in the chopped strawberries and rhubarb. Add in strawberry jello (or 1 tbsp cornstarch & 1 tbsp sugar) and mix together. This helps absorb some of the juices.
2 cups strawberries, 2 cups rhubarb, 1 tbsp strawberry jello
Once the crust has been baked, sprinkle the fruits on top. Then add the streusel. Place back into the oven at 350℉ and continue to bake for 30-35 minutes.
You'll know it's ready when it is a light golden brown. Allow to cool, slice, and enjoy!