Let all refrigerated ingredients come to room temperature, that includes butter, egg and sour cream.
Preheat oven to 350°F.
Measure out flour, salt and baking soda into a small bowl, mix well to distribute thoroughly.
Add sugar and lemon zest to the stand mixer bowl, rub together until fragrant and sugar turn a light yellow.
Add soften butter to the sugar mixture and beat with the whisk attachment until combined.
Add egg, sour cream and lemon extract to the butter mixture and beat again until combined.
Reduce mixer speed to low, and slowly add the flour mixture, mix only until the flour is incorporated to avoid over mixing.
Spray the mini bundt pans with a thin layer of nonstick cooking spray and divide the batter evenly among four pans.
Tap the pans to level the batter.
Place the pans on a large baking sheet and bake for 28 to 29 minutes in the middle oven rack.
Check doneness by inserting a toothpick in the middle of the cake, if the toothpick comes out clean, it is done.
Remove from the oven, and place the bundt pans on a wire rack to cool.
When the bundt pans are cool enough to touch, flip them over and tap to loosen the bundt cake onto the wire rack, let cool completely before adding icing.
To make icing, whisk together the lemon juice with powder sugar, adjust the amount of powder sugar to achieve the desire texture of the icing, thinner icing at 1 ½ cup and thicker icing at 1 ¾ cup.
To ice the bundt cake, flip them over and dip them into the bowl of icing, then place them back on the wire rack to let the icing harden. Garnish with more lemon zest if desired.