Preheat the oven to 350 degrees F. Butter an 8-inch square baking pan.
Add the flour, both sugars, oats and salt to a bowl in your stand mixer. Add in the butter and egg and beat at low speed. Stop the machine and scrape the bowl down a couple of times. Keep processing until the mixture resembles coarse crumbs. Keep 2 cups crumb mixture aside.
Press the remaining crumb mixture on the bottom the prepared pan. Spread the Raspberry Preserves over top, leaving 1/2-inch border. Crumble the rest of the oat mixture over the preserves.
Bake until lightly browned, 40 to 50 minutes. Cool completely before cutting into bars.
Put your raspberries and 1/4 cup water in a saucepan over medium heat. Once it's at a simmer, partially cover and cook 8 to 10 minutes. Pass the berry mixture through a food mill and measure the liquid that remains. You need 3 1/2 cups. Add more water if there isn't enough.
Put the berry liquid into a new saucepan over medium heat and bring to a simmer again. Once it simmers, start adding your sugar in 1/2 cup increments. Give it a stir to incorporate and bring it back to a simmer before adding of the next 1/2 cup sugar. Once the last 1/2 cup is added, bring the liquid to 216 to 218 degrees F on a candy thermometer. Stir constantly.
Let this cool to room temperature prior to using. If not using right away, refrigerate for up to 1 week. Yield: 2 cups.