Melt the butter in a medium pot over medium heat. Add vanilla extract and cornstarch and whisk.
Stir in the granulated sugar, brown sugar, cinnamon and salt and stir once again.
Let the sugar melt down for 5 minutes, stirring.
Then add the peaches.
Stir and cook for 10-12 minutes or until the peaches become cook down, become soft and the filling has thickened. Be patient here, it just takes time and you can't rush it. Don't walk away from the pot since it needs to be stirred regularly.
Remove the pan from the heat and bake in a crust or let it cool completely before storing in an airtight container in the refrigerator for up to 5 days.
Notes
Please refer to my FAQ’s and ingredient list above for other substitutions or for the answers to the most common questions.
If the peaches have fully softened and you haven't noticed it thicken up yet, turn the heat on high. This will activate that cornstarch to get it to thicken.
You can use this is other desserts or toppings, see above for ideas.
This can be frozen, see how to do that above.
This uses about 6 peaches (maybe only 5 if they are very large peaches) and produces about 4 cups worth of filling. Weighing the peaches will give you better accuracy.