Ah, Limoncello.  Truly like drinking sunshine.  I have made it with vodka, I have made it with whiskey.  I've made it with infused simple syrup, including herbs like chamomile and lemon balm in with the sugar and water.  Some people make Limoncello using only the lemon zest and don't include the juice, but I think adding the lemon juice makes it delightful.  I realize that purists might be horrified by my modifications, but what can I say?  I love to experiment.
Limoncello traditionally is made from Sorrento lemons, from the Amalfi coast of Italy.  Southern Italy is famous for producing this sunny yellow liqueur.  Since I live in California, where the Mediterranean climate guarantees ripe delicious citrus almost year round, this is the perfect aperitif to create from Meyer or Eureka lemons.

The following is my basic recipe.  You can add the lemon juice or just use the zest.  It's up to you.

Pour 1 3/4 cup of vodka into a large jar or bottle, leaving some space as the lemon zest will displace the liquid.

Add the zest of 8 - 10 lemons.  This is important - do not peel the lemons and use the rind.  Zest the lemons using a vegetable peeler or grater.  Either one works, depending on if you want large pieces or finely grated pieces of lemon zest.  (I prefer large pieces.  It's easier to clean up once you strain the liquid.) We only want the yellow part of the rind for the infusing process - the white pith will make it bitter, and you don't want that.

Now you must exercise patience and restraint, for the zest needs to steep in order to infuse the alcohol with its oils, which will impart both a lemony flavor and a bright yellow color.  I like to wait at least three weeks.  Shake the bottle or jar once a day, and keep it in a cool dark place while the magic happens.  If you are going to skip the juice, I would let the zest steep in the alcohol for three months as opposed to three weeks.

After I zest the lemons, I like to juice them and then freeze the juice, as lemons will mold quicker once the skin has been removed.  This way, the (strained) juice is all ready to go once you're set to finish your Limoncello.

After you have let the alcohol steep for three weeks, start by taking taking the lemon juice out of your fridge.  Then strain the alcohol by pouring the infused vodka through a mesh strainer.  Discard or compost the zest.

If you froze your lemon juice, make sure that it is completely thawed out.  Take one cup of the juice and combine it with the alcohol.  I usually do this in a large mixing bowl.  Set aside.

Now it's time to make the simple syrup, which consists of sugar and water.  Combine one cup of water with 1/2 cup of sugar in a saucepan.  Bring to a boil, and then simmer for three more minutes.  Turn off the heat and let cool completely.  When the syrup is cool, add it to the vodka and lemon juice mixture.  Stir.
It's natural to see some sediment even if you strained the pulp out of the lemon juice.

Now you can taste your liqueur.  I like my Limoncello to be on the tart side, so if you like it sweeter, you may want to add more simple syrup, little by little, until it is to your liking.  In small batches, carefully pour the mixture through a funnel into bottles and let sit for a week before enjoying.  I recommend keeping your Limoncello in the freezer - because of the alcohol, it will not freeze.  Now even when it's raining outside, you can enjoy a glass of sunshine.