Lemon Pastry Cream (French Crème Pâtissière au Citron)

This silky smooth lemon pastry cream takes advantage of both the fruit's flavourful zest and bright juice to produce a custard that's rich and thick and tastes like sunshine. Because the acid in the juice reduces the thickening power of the cornstarch, this recipe calls for more cornstarch and an extra egg yolk compared to a classic vanilla pastry cream recipe. This recipe takes advantage of two flavouring techniques: the zest is infused into hot milk to quickly extract its aromatic lemon oils, which are largely responsible for a lemony flavour. The juice, on the other hand, is whisked in at the end, after the paste cream has cooled down, helping to preserve its fresh flavour. The resulting pastry cream is versatile enough to pipe into a cream puff, fill a tart shell, or spread between the layers of a cake.

4 oz (½ cup) granulated sugar (115 g)
1¼ oz (3 Tbsp. + 2 tsp.) cornstarch (35 g)
¼ tsp. Diamond Crystal kosher salt or for table salt, use half as much by volume
3½ oz yolks from 5 large eggs, straight from the fridge (95 g)
2 cups whole milk (455 g)
1 Tbsp. (1/8 oz) lemon zest, freshly grated, from 2 large lemons (4 g)
1 oz (2 Tbsp.) unsalted butter, cut into ½" cubes (30 g)
2 Tbsp. lemon juice, freshly squeezed (30 mL)

Special Equipment:
2 qt stainless steel saucier
balloon whisk
fine-mesh strainer

In a large bowl, set up an ice bath by partially filling it with a combination of cold water and ice. Set aside.

In a medium heatproof mixing bowl set on top of a dampened towel (this serves as a stable base), stir together sugar, cornstarch, and salt. Whisk in egg yolks until mixture is pale yellow, smooth, and fluffy, about 1 minute.

In a 2 qt stainless steel saucier, combine milk and lemon zest. Bring to a bare simmer over medium heat.

Remove milk from heat. While whisking continuously, slowly pour milk into egg yolk mixture in a thin stream until all of it has been added.

Return the mixture to the same saucier. Cook over medium heat, whisking constantly until pastry cream begins to thicken, about 2 minutes. Once it thickens, continue to whisk, pausing every few seconds to check for bubbles, about 1 minute. When it begins to bubble, set a timer and continue whisking for 1 minute. This step is important to neutralize starch-dissolving protein found in egg yolks.

Off-heat, whisk in butter until melted and thoroughly combined. Strain pastry cream through a fine-mesh strainer set over a medium heatproof bowl. Immediately place plastic wrap or buttered parchment paper directly on the surface of the cream to prevent a skin from forming. Transfer bowl to prepared ice bath to chill for 30 minutes, then refrigerate until cold, about 2 hours.

When you are ready to use the pastry cream, add lemon juice and whisk until smooth.

Makes 3 cups.

Make-Ahead and Storage:  Pastry cream can be stored in an airtight container, with plastic wrap or buttered parchment paper placed directly on the surface, and refrigerated for up to 3 days.