- Preheat the oven to 350 degrees F.
- Butter an 8-inch square baking pan.
- Add the flour, brown sugars and 1/2 cup of granulated sugar , oats and salt to a bowl in your stand mixer.
- Add in the butter and beaten 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.
- Meanwhile make Raspberry Preserve: Put 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 1-3/4 cup of 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.
- Press the remaining crumb mixture on the bottom the prepared pan.
- Spread 1 cup of 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.