Pulse flour, 1 tbsp sugar, and salt in a food processor or whisk in a large bowl. Cut in cold cubed butter until pea-sized crumbs form, then gradually add ice water until dough comes together. Wrap and chill for 30 minutes.

In a medium bowl, combine the chopped rhubarb, 0.5 cup granulated sugar, cornstarch, lemon juice, and vanilla extract. Mix well to coat the rhubarb.

Preheat oven to 375°F (190°C). Roll out the chilled dough to about 1/8-inch thickness, then cut into circles using a round cookie cutter. Press each circle into the cups of a 24-cup mini muffin tin and spoon the rhubarb filling into each.

Bake for 20-25 minutes, or until the crust is golden brown and the filling is bubbly. Let the tarts cool completely in the muffin tin on a wire rack.

While tarts cool, whisk together honey, powdered sugar, and milk in a small bowl until smooth. Once tarts are completely cool, drizzle the honey glaze over each tart before serving.