Begin by melting butter in a medium saucepan over low heat (140°F/60°C). Add your condensed milk, sugar, and mashed ube, then stir continuously until everything is well combined. Cook this mixture for 5-10 minutes until it thickens nicely. For an extra smooth texture, you can press it through a fine-mesh strainer. Let this mixture cool completely before moving forward.
While waiting for your ube mixture to cool, cut your spring roll wrappers in half diagonally. Once the filling has cooled, place about 1½ tablespoons of the ube mixture in the center of each wrapper. If you're using any add-ins like macapuno or langka, place them on top of the ube filling now.
To wrap your turon, fold the bottom corner over the filling, then fold in both side corners. Roll everything upward tightly, making sure to keep the filling secure. When you reach the top corner, dab it with a little water to seal it closed. Repeat this process with all your wrappers.
Now heat your vegetable oil in a deep frying pan or wok until it reaches 350°F (175°C). You can test if the oil is ready by dipping the handle of a wooden spoon in it – if small bubbles form around the handle, your oil is ready. Sprinkle 2-3 tablespoons of sugar over the surface of the oil.
Carefully place your turon in the hot oil, working in batches to avoid overcrowding. Fry them for about 3-4 minutes per side until they turn a beautiful golden brown color. Keep the heat at medium to prevent the sugar from burning.
Remove your turon with a slotted spoon or spider strainer and place them on paper towels to drain any excess oil. Let them cool for just a minute or two – they should still be warm when served.
Serve your ube turon right away while they're still hot and crispy. You can enjoy them plain, drizzled with condensed milk, or with a scoop of vanilla ice cream on the side. For the best experience, eat them within a few hours of frying while the wrapper is still crispy.