Make the crust: Preheat your oven to 350 degrees F. Spread out 1/2 cup of slivered almonds on a baking sheet. When the oven is ready, toast the almonds for about 5-6 minutes, opening the oven to stir the almonds around every 2 minutes. The almonds are done when they are light brown and smell like heaven. Remove from the oven and set aside to cool. 

Meanwhile, add 12 full graham cracker sheets to a food processor and pulse into fine crumbs. (You could also buy a box of graham cracker crumbs. You need 1 and 1/3 cups. If you are skipping the almonds, add 1/2 cup crumbs.)

Add 2 tablespoons sugar and 1/4 teaspoon salt. Add the toasted almonds to the food processor and pulse into fine crumbs. Add 6 tablespoons melted butter and pulse until the mixture resembles wet sand.**

Press the mixture into a 9 or 9 and 1/2 inch pie plate. I like to use a glass to press it. Make sure it goes as far up on the sides as you can get it to go. (So that the custard doesn't overflow)

Bake the crust at 350 for 10 minutes. Set aside to cool completely before adding the filling (I often stick mine in the fridge/freezer after it has cooled from the oven. If your pan is glass, you should be able to touch the pie plate with your hands before refrigerating (you don't want to crack the glass from the temperature change)

Make the lime custard: Add 6 egg yolks to a large bowl or stand mixer. Beat on medium high speed for about 5 minutes. Your yolks will lighten to a pale yellow color. (You're whipping air into them to make them nice and fluffy. Don't skip it.)

With the mixer running, add in the sweetened condensed milk. You need 1 and 1/2 (14-ounce) cans. This is 1 full can plus 2/3 cup from a second can. (use the remainder to make these Buried Cherry Cookies!)

Add 1 cup plus 2 tablespoons full fat sour cream and combine well.

Zest about 5 or 6 limes until you have 2 and 1/2 tablespoons. Do yourself a favor and buy a Microplane zester for this job. This tool is so sharp and makes zesting a breeze. Add the zest to the bowl.

Juice your limes until you have 1 cup plus 2 tablespoons. I used an electric citrus juicer, which makes it so fast. It's a worthy investment if you love citrus, or if you plan to make this pie!

Add 1 cup plus 2 tablespoons lime juice to the custard mixture and beat until just combined, scraping the sides and bottom of the bowl until you're sure it's all mixed in.

Pour the custard into the cooled crust. Pour SLOWLY to make sure it doesn't overflow.

Bake the pie at 350 for 25 minutes. You should see a few tiny bubbles on the surface of the pie. The pie will not look set and will be very wiggly. Never fear! It's supposed to be like that.

Remove from the oven and let cool on a cooling rack for about 45 minutes to an hour.

Cover the pie with plastic wrap and chill in the fridge for at least 3 hours. (You can make this pie up to 3 days ahead of time.)

Make the whipped cream: When you are ready to serve the pie, beat 1 and 1/2 cup whipped cream on high speed. With the mixer running, add the juice from 1 lime (do it while mixing to make sure you don't curdle the cream)

Add 1/3 cup powdered sugar and continue beating on high speed for 2-3 minutes, until the cream is stiff.

Add the whipped cream to a piping bag set with a large star tip. (Or you could put it in a ziplock and snip the corner.) Pipe the whipped cream on top of the pie however you like. Save any remaining whipped cream for guests to add to their own slice. See note for alternative topping.

Garnish the pie with sliced limes and additional lime zest.

After decorating, you can freeze the pie for about 15 minutes before serving. Key Lime Pie is best served very cold!