Toast almonds in a dry skillet over medium heat for about 3 minutes, stirring constantly, until lightly golden.

Remove toasted almonds to a plate to cool completely; freezing speeds up the process.

In a food processor, combine flour, confectioners' sugar, and salt; pulse to mix and break up lumps.

Add cooled almonds and pulse for 30 seconds to incorporate.

Add cold, sliced butter and pulse until the mixture resembles small clumps.

Add lightly beaten egg and pulse in long increments until the dough comes together in a few balls.

Lightly flour your workspace and spray a 9-inch tart pan with a removable bottom with nonstick spray.

Remove dough from the food processor and knead lightly a few times to incorporate all ingredients; form into a flat disc.

Press the dough evenly into the prepared tart pan.

Chill in the freezer for 30 minutes.

Preheat the oven to 350 degrees F (175 degrees C).

Remove the tart from the freezer and place it on a baking sheet.

Prick the bottom of the tart all over with a fork.

Line the tart with parchment paper and cover with pie weights (or dried beans).

Bake the crust for 25 minutes.

Remove the tart from the oven, remove the parchment and pie weights, and bake for 2 more minutes.

If the tart has puffed up, gently press it down with a spoon.

While the crust bakes, whisk together granulated sugar, lemon juice, salt, and eggs in a heavy-bottomed medium saucepan off the heat.

Place the mixture over medium heat and cook, stirring constantly, until the curd thickens (about 8 minutes) and reaches 170 degrees F (77 degrees C).

Whisk in the butter piece by piece until smooth.

Pour the lemon curd into a large measuring cup.

Remove the baked crust from the oven and carefully pour in the lemon curd, filling just below the top of the tart.

Bake the tart until the curd is set (about 10 more minutes).

Remove from the oven and let cool completely before serving.

Remove the tart ring and slice into pieces.

Garnish with confectioners' sugar if desired.