In medium bowl, whisk together flour, brown sugar, cinnamon and salt.

Using a pastry blender or 2 butter knives, cut in butter until combined but still crumbly.

Cover and refrigerate at least 30 minutes or up to 5 days before using.

Preheat oven to 350°F. Line muffin pan with paper liners. In small bowl, whisk together tea, flour, lemon zest, baking powder, baking soda and salt.

In mixing bowl, beat butter and sugar at medium-high speed 3 minutes or until light and fluffy. Add egg and beat until well combined, scraping down side of bowl as needed. Add vanilla; mix at low speed until incorporated. Add sour cream and flour mixture all at once; mix at low speed until just combined.

Divide batter evenly among prepared muffin cups. Divide half of streusel over batter; use back of spoon to gently press streusel into batter. Evenly sprinkle remaining streusel over muffins. Transfer to oven and bake 22 to 24 minutes or until toothpick inserted in center of muffin comes out clean. Transfer pan to wire rack to cool.

In small bowl, whisk together powdered sugar, lemon juice and milk.

If needed, add additional milk one teaspoon at a time until you have a very thick but pourable glaze.

Place muffins on wire rack set over rimmed baking pan; drizzle evenly with glaze.