Whisk flour, baking powder, sugar, and salt together in a large bowl. Cut in the 6 tbsp cold cubed butter with a pastry cutter or your fingertips until the mixture resembles coarse crumbs with a few pea-sized butter pieces remaining, about 2 minutes.

Pour in the 3/4 cup cold whole milk and stir with a fork just until no dry flour remains, about 20 to 30 seconds. Turn out onto a floured surface and fold the dough over itself 4 to 5 times without kneading.

Pat the dough to 3/4 inch thick and cut with a 2.5-inch round cutter, pressing straight down without twisting, for about 8 biscuits.

Preheat oven to 425°F (220°C). Place biscuits touching on a parchment-lined baking sheet and bake for 12 to 14 minutes until golden brown. Cool on the pan for 5 minutes.

Whisk the 1 cup powdered sugar, 3 tbsp strawberry jam, 1 tbsp milk, and 1/4 tsp vanilla extract until smooth. Spoon over the warm biscuits and serve with the glaze just beginning to set.