Preheat and prep: Set your oven to 350°F (175°C). Grease and line a 9×13-inch baking pan with parchment paper for easy removal later.
Make the dough: In a large bowl, cream together the butter and sugar until light and fluffy (about 2–3 minutes). Beat in the eggs and vanilla. In a separate bowl, whisk together flour, baking powder, and salt, then slowly add to the wet ingredients until a dough forms.
Build the base: Press about two-thirds of the sugar cookie dough evenly into the prepared pan.
Prepare the filling: Pick the strawberry pieces out of your strawberry pie filling with a fork and leave most of the syrup behind so the bars do not get soggy. You want a little bit of syrup for moisture, but certainly not all of it. I removed around ¾ cup of syrup total.
If the strawberry pieces are large, chop them into bite size pieces. Stir in the lemon juice. If the mixture seems too watery, add a bit of cornstarch.
Add the filling: Spoon the strawberry mixture over the cookie dough and gently spread it into an even layer.
Swirl with dough: Drop small spoonfuls of the remaining dough across the top of the apples, leaving little gaps so the filling peeks through.
Sprinkle the topping: In a small bowl, stir together the cinnamon and sugar, then sprinkle evenly over the top.
Bake: Bake for 35-45 minutes, or until the cookie dough is set and golden brown. The middle might look a little soft but will firm up as it cools.
Slice: After completely cool, slice into bars. Serve at room temperature, or slightly warm with a scoop of vanilla ice cream if you want a strawberry pie dessert moment in bar form.
