In a medium saucepan, melt butter over medium low heat.
Add sugar and bring to a boil. Turn the heat down to low and simmer the mixture for about 2 minutes, stirring constantly.
Stir in 1 tablespoon of milk.
Heat to boil.
Take of the heat, cool for 5 minutes. Transfer into a medium mixing bowl.
Cool to lukewarm, about 30 minutes.
If the sauce hardens, microwave for 5 to 10 seconds.
Add powdered sugar and whisk. If the mixture is crumbly, add another tablespoon of warm milk.
Whisk until drizzling consistency.
to make the crust:
Grease an 8" square pan. Line with parchment paper and grease the sides and the bottom. Set aside.
Preheat the oven to 375 degrees F.
In a medium mixing bowl, whisk melted butter with sugar. Add remaining ingredients and stir everything until a thick dough forms. Reserve ¾ of a cup for the crumb topping.
Press the remaining dough onto the bottom of prepared pan.
to make the filling:
In a medium mixing bowl, whisk all ingredients until smooth.
Pour over the crust.
Top with little bits of the reserved dough to make the crumb topping.