In a large bowl, combine 1.75 cups all-purpose flour, 0.25 cup powdered sugar and 0.25 tsp salt. Add 0.5 cup cold cubed unsalted butter. Using a pastry cutter or your fingertips, cut the butter into the flour until the mixture resembles coarse crumbs with some pea-size butter pieces remaining.

Bind and chill

Stir in 1 egg yolk and 1 tablespoon cold water just until the dough comes together (add up to 1 teaspoon more water if dry). Do not overwork. Form a disk, wrap in plastic, and refrigerate for at least 30 minutes.

Blind-bake shells

Preheat oven to 350°F (175°C). Roll chilled dough on a lightly floured surface to about 1/8-inch thickness. Cut into rounds or tartlet shells to fit six 3-inch tartlet pans (or 6 small ramekins). Press dough into pans, trim excess. Prick bottoms lightly with a fork. Line with parchment and fill with pie weights or dried beans. Bake 12 minutes, remove weights and parchment, then bake another 6–8 minutes until golden and set. Let cool completely before filling.

Apple Jam

Prepare apples

Peel, core and dice apples until you have about 3 cups. Combine apples, 0.25 cup water, 0.75 cup granulated sugar, 1 tablespoon lemon juice and 0.5 teaspoon ground cinnamon in a medium saucepan.

Cook to jam consistency

Bring mixture to a simmer over medium heat, stirring occasionally. Reduce heat to medium-low and cook, stirring frequently and mashing some pieces with the back of a spoon, until apples are very soft and mixture thickens to a jam (about 20–25 minutes). If using, sprinkle in 0.5 tsp pectin about 5 minutes before finishing and stir to incorporate. Taste and adjust sugar or lemon if needed. Remove from heat and let cool to room temperature.

Chestnut Mont Blanc Paste

Make chestnut paste

Place 10 oz cooked chestnuts in a food processor. Add 0.25 cup heavy cream, 0.5 cup powdered sugar, 0.5 teaspoon vanilla extract, 2 tablespoons softened butter, and 1/8 teaspoon salt. Process until very smooth, stopping to scrape down sides. If the paste is too stiff, add additional teaspoonfuls of cream (up to 2 tablespoons more) until pipeable but not runny. Transfer paste to a piping bag fitted with a small round or multi-holed Mont Blanc tip (about 5–7 mm opening).

Filling & Assembly

Whip cream

Chill a mixing bowl and whisk. Pour 0.75 cup cold whipping cream into the bowl and add 1 tablespoon powdered sugar. Whip to soft peaks (be careful not to overwhip).

Fill tart shells

Spoon about 1 to 1.5 tablespoons of cooled apple jam into the bottom of each cooled pastry shell, spreading gently to an even layer (total about 0.75 cup jam across all shells).

Pipe whipped cream

Top the jam with a small dollop of whipped cream (about 1 tablespoon each) to give the Mont Blanc paste a base to adhere to.

Pipe chestnut strands

Using the prepared chestnut paste in the piping bag, pipe slender continuous strands over each tart in a mountain shape (start at the outer edge and spiral up toward the center) until each tart is covered and a small peak forms. The goal is the classic Mont Blanc look — layered thin chestnut ropes forming a peak.

Finish and garnish

Dust each tart lightly with 1 teaspoon powdered sugar total (just a light dust across all tarts) and sprinkle with toasted sliced almonds if using. Chill the assembled pastries for at least 30 minutes to allow flavors to meld and chestnut paste to set slightly. Serve chilled or at cool room temperature.