Preheat oven to 350°F. Line a 9x9 baking pan with parchment paper, leaving some hanging off opposite edges. This will make the bars easier to lift from the pan.
In a large bowl, add the flour, granulated sugar, baking powder, salt, and cardamom. Whisk until well combined. Add the cold, cubed butter. Use two forks to break apart the pieces of butter. Then, gently use the tips of your fingers to rub the butter into the dough until you have pea-sized crumbles.
Place the dry pie dough ingredients into the fridge to stay cool while you make the filling. In a medium bowl, add the pitted cherries, sugar, corn starch, lemon zest, lemon juice, and orange liqueur. Mix together well and set aside.
Remove the dry ingredients from the fridge. Whisk together the egg, milk, and vanilla extract. Drizzle it over the dry ingredients, then mix together using a spatula or wooden spoon until incorporated. The mixture should look like wet sand and still be a little crumbly.
Take 2/3 of the pie dough and press it evenly onto the bottom of the baking tray. Spread the cherry filling evenly over the dough. Crumble the remaining 1/3 of the dough over the filling. Then, sprinkle the surface with the rolled oats.
Place the baking tray in the middle rack of the oven and bake for 40 - 45 minutes until the top is a light golden brown. Remove from the oven and let cool completely. I usually let the bars cool at room temperature for 30 minutes then place in the fridge for the rest of the time.
Remove from the tray and cut into 16 squares. Store leftover bars in covered containers in the fridge.