Spray a 6 cup (7 inch) bundt pan with cooking spray. Lightly flour with 1 tbsp flour, shaking out any excess flour into the trash.
Mix cake mix, milk, melted butter, and eggs using a mixer for 1 minute on medium-low speed. Scrape the sides of the bowl to incorporate any remaining flour, and mix again on medium-low for 1 more minute. Do not overmix! Set aside.
In a separate bowl, coat raspberries in 1 tsp flour, tossing any remaining flour in the trash. Fold raspberries gently into the cake batter.
Pour cake batter into the prepared bundt pan. Smooth out the batter using a rubber spatula. Cover the cake with a double layer of paper towels, then cover tightly with aluminum foil.
Pour 1 1/2 cups of water into the bottom of your pressure cooker. Place the bundt pan onto the wire rack trivet and lower it into the pressure cooker using the handles. Place the pressure cooking lid on top and set it to the sealing position.
Set the pressure cooker to high pressure for 40 minutes. It will take about 15-20 minutes to get to full pressure.
After the cake is done cooking, allow it to naturally release pressure for 5 minutes, and then quick release any remaining pressure. When all pressure has been released, carefully remove the trivet and bundt pan using pot holders. Remove the tin foil and paper towels and allow the cake to cool for 10 minutes in the pan.
After 10 minutes, carefully turn the bundt pan over onto a wire cooling rack and allow the cake to fully cool, about an hour or two, before transferring to a serving platter for glazing. This is important. If the cake is still warm, the glaze will melt off and won't harden properly.