For the Muffins:

1. Preheat the oven to 375°F and line a 12-cup muffin pan with paper liners. Spray the liners with nonstick baking spray.
2. In a medium bowl, whisk together the flour, baking powder, and salt.
3. Using a hand or stand mixer, beat the butter and sugar together until pale yellow and fluffy, about 2 minutes.
4. Add the eggs and vanilla extract and beat until smooth.
5. Alternate adding the flour and the milk, starting and ending with flour (so, add flour first, then milk, then flour, and so on).
6. To the empty flour bowl, add the blueberries and 1 tablespoon flour. Toss the berries to evenly coat in the flour.
7. Using a spatula, gently fold the berries into the batter. Scoop the batter into the prepared muffin pan and then prepare the streusel.

For the Streusel:

1. Melt the butter in a small saucepan and then add in the other ingredients.
2. Cook over medium-low heat, stirring almost constantly, for about 5 minutes. It is ready when it is very crumbly and the butter has been completely absorbed. Sprinkle the streusel generously over the muffin batter once it is cool enough to handle.
3. Bake the muffins for 20-25 minutes or until they are set in the middles and golden around the edges.
4. Allow to cool on a wire rack and keep covered at room temperature in an airtight container.

For the Chai Butter:

1. While the muffins are baking, make the chai butter by mixing all the ingredients together in a bowl, stirring until everything is evenly incorporated.
2. Serve the muffins with the chai butter.