*Make your cherry filling at least an hour before prepping your other ingredients so it has time to cool*
Starting with the cherry pie filling, mix together the cornstarch and water in a medium pot. Add your cherries, sugar, lemon juice, and a pinch of salt to the pot and stir. Place over medium heat, stirring regularly until thickened. About 8-10 minutes
Remove from heat, pour into a bowl, and cool completely. After a few minutes at room temperature, you can store it in the fridge to cool faster, just stir it once in a while if you do so it cools evenly
Preheat oven to 350°F. Grease a 9-inch pie dish
For your cake, add all of your dry ingredients to a bowl - sugar, flour, salt, baking powder - and mix. Then add in your softened butter and beat with a mixer until it resembles coarse sand. It’s important all the dry is mixed in at this step
In a separate bowl, beat together your eggs, vanilla, and milk. Pour half of your mixture into your butter/dry mix and beat together for 30 seconds. Then add the remainder of your liquids and mix just until combined.
Pour your batter into your greased dish and spread evenly across the bottom
At this stage, we’re going to partially bake our cake. Place it in the oven to bake for 12 minutes. It should be set on the sides, but still a bit wobbly in the middle. Remove and leave to cool down a bit while you make your pie crust
For your pie dough, add your flour and salt to a bowl and stir. Cut or rub your cubed butter into the mixture until it resembles coarse sand. Add in your cold water, stir, and start to compress your dough into a ball
Place your dough between two sheets of parchment paper and roll to a ⅛” thick circle. Place in the fridge to chill for at least 10 minutes
Remove your pie dough from the fridge and carefully peel off the parchment paper. Use a pizza cutter or pastry wheel to cut 1-inch strips
To assemble, carefully spoon the cooled cherry filling over the cake, leaving a small 1/4" border. Lay a few of your strips of pie dough vertically across the top of your filling, leaving about an inch of space between. Horizontally weave over and under your remaining strips of dough, one at a time, leaving about an inch of space between each row. Remove the extra overhang of dough off each row/column, then use the remaining strips/excess of dough and line the rim of your pie to form your crust. Fold under as needed to get a thicker border. Crimp using your fingers if desired.
Pop your pie in the fridge for 5 minutes
Drop your oven to 325°F
In a bowl, beat your egg yolk with a splash of milk until combined. Brush your egg wash over your dough and sprinkle with coarse sugar
Bake 50-60 minutes until puffed and the crust is light golden
Allow to cool for 1 hour before serving