Heat the oven to 350 degrees and coat a 9-by 13-inch baking dish with butter. In a medium bowl, whisk together the first six ingredients.
With a hand mixer or a stand mixer with paddle attachment, beat the butter until smooth. Add the dry ingredients, and blend at medium speed until the mixture resembles coarse crumbs, about 1 minute. Reduce the mixer's speed to low and add the eggs, one at a time, until just blended. Slowly add the buttermilk and blend evenly.
In a large bowl, stir together the prepared batter with the corn, scallions, and jalapeno until just blended.
In a large pan over medium heat, warm 2 tbsp. olive oil. Scoop 1/4 cup of batter, drop it into the pan, and flatten it slightly. Repeat with three more scoops. Cook the fritters until golden brown, about 4 minutes per side.
Transfer the fritters to a cooling rack or paper towel-lined plate. Repeat with the remaining batter, adding more olive oil as needed. Serve them warm, with salsa on the side.