Add the softened butter, sugar, and flour. Use a fork or a spoon to mix the flour and sugar into the butter until small clumps begin to form. It should look like clumpy white sand.
For the muffins, first add the softened butter to a large bowl with the sugar and beat well with a mixer. Do this for a few minutes until the butter is light and creamy.
Add the greek yogurt, eggs, vanilla, and lemon juice to the bowl. Mix well until the eggs are fully incorporated into the batter.
Add the flour, baking soda, baking powder, and lemon zest to the bowl and gently fold into the batter. Don't over mix this step and only mix until no flour clumps remain.
Add the blueberries to the batter and fold to disburse. Set the bowl aside while you prepare the cream cheese mixture.
Add the softened cream cheese to a medium-sized bowl the the sugar and egg yolk. Beat well until light and creamy.
Place muffin liners into a muffin tin and fill each almost to the top with the muffin batter. Add ½ Tablespoon of the cream cheese mixture on top and swirl it into the muffin batter with a thin knife or toothpick.
Sprinkle a handful of the streusel crumble on top of each muffin. Then bake in the oven until golden brown around the edges and set in the middle.