Lower the oven rack to the lower-third position and preheat the oven to 350°F (177°C). Grease an 8×4-inch loaf pan with nonstick spray. Or you can use a 9×5-inch loaf pan for a shorter loaf.

Whisk the flour, baking powder, and salt together in a large bowl. Set aside.

With a handheld or stand mixer fitted with a paddle or whisk attachment, beat the butter on high speed in a large bowl until smooth and creamy, about 1 minute. Add the granulated sugar and beat on high speed for 2 minutes until creamed. Scrape down the sides and up the bottom of the bowl as needed.

With the mixer running on low speed, add the eggs one at a time. Once the last egg is completely mixed in, stop the mixer. Add the sour cream, lemon juice, lemon zest, and vanilla extract, then beat on medium speed until combined. Scrape down the sides and up the bottom of the bowl as needed.

With the mixer running on low speed, slowly add the dry ingredients just until combined. If needed, run a whisk through the batter a few times to rid any large lumps. Avoid over-mixing. Batter is very thick.

Spoon/spread the batter into prepared loaf pan and bake for 55-65 minutes if you used an 8×4-inch pan and 45-60 minutes if you used a 9×5-inch loaf pan. Tent the cake with aluminum foil halfway through baking to prevent the top from over-browning.

Remove the cake from the oven and place on a wire rack. Allow cake to cool in the pan on the wire rack for 1 hour, then carefully remove the slightly warm cake from the pan. Let it continue cooling on a wire rack or on a serving plate/platter.

Whisk all of the icing ingredients together and pour over cake. Serve immediately or wait until the cake cools completely.

Cover and store leftover cake for up to 3 days at room temperature or up to 1 week in the refrigerator.