Pastry: In bowl, whisk flour with salt. Using pastry blender or 2 knives, cut in butter until mixture resembles coarse crumbs. In liquid measure, whisk egg yolk with vinegar; pour in enough ice water to make 1/3 cup. Drizzle over flour mixture; stir briskly with fork, adding up to 2 tbsp more ice water if needed, just until dough comes together. Shape into disc; wrap in plastic wrap. Refrigerate until chilled, about 30 minutes. (Make-ahead: Refrigerate for up to 2 days.)
On lightly floured work surface, roll out dough to scant 1/8-inch thickness. Using 5-inch round cookie cutter, cut out 8 rounds, rerolling scraps as necessary. Fit into 8 lightly greased fluted 4-inch mini tart pans with removable bottoms. Prick crusts all over with fork. Refrigerate until firm, about 15 minutes.
Line crust with foil and fill with pie weights or dried beans. Bake on bottom rack of 400°F oven for 8 minutes. Remove pie weights and foil; bake until golden, about 5 minutes. Let cool slightly in pans.
Filling: While crust is cooling, in bowl, whisk together almonds, flour, sugar, and salt; whisk in eggs until combined.
In heatproof bowl set over saucepan of gently simmering (not boiling) water, melt chocolate and butter, stirring, until smooth; stir into almond mixture. Scrape into crusts.
Arrange pears, overlapping slightly, over top of filling. Bake on bottom rack of 375°F oven until filling is puffed, about 18 minutes. Let cool completely in pans.
Sugar Crackle: While tartlets are cooling, in small saucepan, stir together sugar, thyme (if using) and 1/3 cup water over medium heat, brushing down side of pan with pastry brush dipped in cold water, until dissolved; bring to boil. Discard thyme. Boil vigorously, without stirring but brushing down side of pan, until amber, about 8 minutes. Immediately drizzle over tops of tartlets. Let stand until set, about 20 minutes.
Change it up: Chocolate Pear Frangipane Tart with Sugar Crackle
On lightly floured work surface, roll out dough into 12-inch circle; fit into lightly greased fluted 10-inch tart pan with removable bottom. Trim to fit. Prick crust all over with fork. Refrigerate until firm, about 30 minutes. Line crust with foil and fill with pie weights or dried beans. Bake on bottom rack of 400°F oven for 15 minutes. Remove pie weights and foil; bake until golden, about 7 minutes. Prepare filling as directed; bake on bottom rack of 375°F oven until puffed, about 35 minutes. Continue with recipe as directed.
Tip from The Test Kitchen: Keep an eye on your sugar syrup as it’s boiling; the colour will change from clear to amber very rapidly, and allowing the syrup to boil any longer can result in a bitter burned taste.
Makes 8 tartlets.